The years 1990-1992 (which is presumably when the election is called) are probably more rocky for the Conservatives, as Heseltine is likely to be less of a peacemaker in the party than John Major was.
That probably means the Conservatives are in a worse shape going into the general election, and so probably lose to Labour. Heseltine probably resigns as leader, and is replaced by... Malcolm Rifkind (assuming he holds his seat), Chris Patten (same deal) or maybe Ken Clarke. Major is a possibility, but he frequently claims in his autobiog that he wasn't interested in leading the Party in opposition, so we'll rule him out. If Hurd wasn't kept in Heseltine's Cabinet, he'll probably be standing down in '92, so we can rule him out. Tebbitt *might* stand, but it seems unlikely.
If the Tories *do* win in 1992, then Heseltine might have an easier run from 1992-1997. By trying to be a peacemaker, I think Major let the party's divisions continue as a running sore. Heseltine might find things rockier up until the election, but if he wins, he'll be vindicated enough that he should be able to hold the Right in check.
If the Tories win, I'd expect Heseltine to retire on health grounds somewhere between 1993 and 1995, probably being succeeded by one of the figures mentioned above, or maybe by Portillo (who has probably made it into Cabinet by this point.) In either case, I can't see the Tories winning in 1996/1997, but hopefully a landslide defeat can be avoided.