No regional area will ever overtake the capital city of every state in this country, some regional area's do better than others, population make that a no brainer, especially as businesses move to the regions, however there are towns in NSW that are growing at good rates, NCLE is deemed to have 457,192, make that 457,200 in case of twins being born by June 2020, thing is not all are living within the Newcastle boundary though but would include the various suburbs that radiate out from there, but how far do you take it?
In Sydney, the current government is pulling up tracks or wanting to, in order to put crewless trains as replacements, interestingly will be how many of the stations now without staff will have them on platforms when the new metro stations open, especially after the incident this week shown on TV news of a woman being caught in the doors as the train pulled out, thankfully a call was made and the train stopped, with the woman being saved. How far the metro's will expand is anyone's guess but, looking at how much the general area that would include Sydney are commuters, yet also have basically poor transport options, especially car parking options at stations which stops many from using PT, will only get worse over time, metro or heavy trains, thing is the Sydney area will grow for years and so will car commuting which this Corona virus will push people back on the road networks, great for the governments as they get more money through tolls. Melbourne and Brisbane, along with the Gold Coast are growing and PT is being expanded in areas where they were not some time back.
Lastly, & I simply repeat in response to what you have said regarding the local lines to/from Maitland, if the bypass goes ahead. There are and will be local pax services along the line, while I could readily name more than a couple of stations that could readily be closed owing to almost no one using them there will be needs for commuter trains for some time to come.
I don't think anyone is expecting any regional area (I hate the word by the way, people think regional = anything that is not a capital, that is wrong, is Newcastle regional? is Wollongong regional? is the Gold Coast regional?), I personally just think that people need a choice about where they can live and still have access to amenities like sustainable employment and convenient public transport, it's completely ridiculous to think that NSW has 800,642 km² of land, and only ONE liveable city!, and people think a high-speed bullet train to give people quicker access to Sydney is the solution, but I doubt these people know much about modern job applications, or maybe they do but ti didn't cross their mind.
Unfortunately our government simply doesn't have our best interests in mind, I don't want to come across as whiny saying this but it's true, whether state or federal, millions are spent on stadiums, sports grants, tax cuts for big business, punishment for the unemployed (google 'cashless welfare card'), etc, but they can never seem to cough up a cent for local jobs (hence the crewless trains and staffless stations you mentioned, or the lack of local manufacturing) or infrastructure that will help those most in need (for example, public transport in places where families can actually afford to live).
Sydney's struggling to cope for the reasons you mentioned about parking, and people were almost falling off platforms at Town Hall station pre-covid, all the more reasons to give residents a choice about there they can live, let me repeat; 800,642 km² of land, 8,117,976 people, ONE liveable city, do people really think this is sustainable? or that a high-speed bullet train is the answer?
Covid-19 combined with the current petrol prices will likely encourage people to use cars more, but ultimately congestion will probably make public transport use rise again,
and young people will probably also be more dependence on public transport with growing youth unemployment/underemployment, and families having less money owing to general unemployment/underemployment caused by Covid-19 and an already crippled economy, will make owning more cars (with the exorbitant insurance premiums for young drivers) unsustainable.
Lastly, by all means the need for commuter trains to Maitland will always be there, likewise the need for commuter trains to other areas of Newcastle including Fassifern/Toronto and Belmont, and a proper bus network, I always see people complaning on the Newcastle Herald Facebook page about the lack of parking in the CBD, can't really blame them when there is no other practical way to get there besides by car,
but our Government does not care about the needs of the people, especially the needs of those on middle/low income, and if history is anything to go off, the cessation of the local commuter trains to Maitland (and Fassifern) is entirely possible should the Newcastle metropolitan area be bypassed with a branch connecting Port Waratah and Kooragang to the bypass.
In my own opinion there should be two Sydney to Melbourne routes and two Sydney to Brisbane routes.Been few of the stops that are supposed to be made at Wondabyne now see any passengers, not sure where there are hiking trails either, but no doubt would be wrong there. Certainly much of the CC line is a hindrance to long distance trains, even the fast ones to Hamilton & return, to eliminate them as you say would be huge & a costly exercise. To even consider tunnelling from even Cowan or closer to Hornsby to have a more direct route would really have crippling costs, having a tunnel and bypassing Woy Woy and the other winding line to Gosford while still expensive would have a lot less cost.
My reasoning for this is that in order to straighten the corridor some places need to be bypassed, if Wondabyne station is bypassed there would be complaints from hikers and campers, if Wondabyne station is not bypassed all the people that want a faster corridor would complain. The same would go for many Central Coast and Southern Highlands stations, Picton is one good example
Rather than have this situation a dedicated high speed rail corridor could be built underground from Parramatta to Maitland and then on to Brisbane bypassing the central coast and shortening the journey times from about 3/4 hours to about 1 1/2 hours (Sydney to Maitland section), whilst also keeping the usual corridor for general passenger use
This plan is probably very uneconomic and expensive and due to that it will probably never happen
Would it be possible to ease some curves between the Hawkesbury River and Wondabnye with some raised embankments? This could speed up travel time, not bypass Wondabyne, and should be relativity cheap, however, it may be prohibited as the area is part of a national park.
From there you could possible tunnel and bypass to Ourimbah to speed up freight, regional, interstate, and Newcastle services, and keep the old line to serve the busy Woy Woy, Gosford, and Wyong, as well as intermediate stations.
Following that it should just be a matter of straightening the curvies between Warnervale and Morisset, and Morisset and Fassifern, from there I would not be opposed to a freight line bypassing the Newcastle metropolitan area if there was a guarantee no one would rip up the tracks between Fassifern and Newcastle.