Pretty ASB with those conditions, though I think Labour would have won in 1987/8 if the SDP had never left, even if the Falklands War still happened.
I don't know, maybe something like Grenada but on steroids happens closer to the election and Thatcher's foreign policy is made to look mad. But I think despite Kinnock's best efforts, voters were still too wary of the skeletons in Labour's closet at this point.
How about a Hung Parliament with the Tories as the largest party?
There's also the possibility of Thatcher being killed in the 1984 assassination attempt; while there would be a sympathy vote, that would largely be forgotten by 1987 and I think Heseltine or whoever would struggle to draw the same vote Thatcher did.