What you are effectively saying is that Delta will buy VS out for its London slots.
But it wouldn't get all of them would it? like BA didn't get all of BMIs.
I suspect no one has quite decided this yet -it is most likely if VS can't be made profitable.
What DL have with VS now is a North Atlantic joint venture- I am sure that will be the focus of the VS strategy and will have to make money.
The crunch will be to see what they do as others say with the holiday business- they could keep Orlando and Las Vegas but ditch/sell the Caribbean routes - they certainly don't fit in with the rest of the operation.
If they ditch Shanghai for a US destination (and I think they will - national CC have apparently been put on to different contracts) - that doesn't tell us much- just more expansion of Joint Venture to say Minneapolis/St.Paul or Cleveland.
If they ditch routes where the slots are pretty useless for the US; Dubai, Delhi and Lagos and to some extent Jo'Burg then we will know the rumours are true. There will then be only one place it can all end.