Glenfield via Granville services will continue to Leppington.
If that's correct, then:
1) blows theory about relevance (sense) of turnout speeds,
2) turnbacks on P3 would cease, but
3) people coming from the direction of Granville would still have to change trains at Glenfield if heading for stations Macquarie Fields to Macarther.
While turnbacks are operating, station announcements at prior stations (like Liverpool for example) should advise passengers to 'Catch this train and cross platform at Glenfield for Campbelltown services.' People generally would have ignored Glenfield terminators in earlier times due to need of climbing/shoving up stairs to another platform, but this is (now) not necessary.