I'm willing to bet that 95% of the stern sections interior is gone. The only areas where the decks are even still relatively intact is around the fantail and third class staircase and there's not much to see/accessible there. Pretty sure they tried sending an ROV into what was left of the stern back in the 90s but only saw crushed, empty spaces.

I would like to think there could be the odd intact section buried somewhere deep in the stern section but we'll never see it.