Well, it depends on whether or not the NDP wins a majority. If they do, than they're most definitely in power until 1992 at least, in which case given the constitutional drama that's likely to occur no matter who's in power, as well as the recession, they likely go the way of Bob Rae's NDP in Ontario - back to third-place for the foreseeable future.
As for the other PODs, it may well end up that the PCs end up as the third-party in 1988. Keep in mind, polls in 1987 (and if I remember correctly, even in early 1988) had the PCs in third, with the Liberals and NDP fighting for first. If the PCs never recover, you could well see the NDP win a minority (if not a majority).
Heck, even a POD as late as the start of the 1988 campaign could result in the NDPs winning a minority. If Turner ran a worse campaign (a campaign more like his disastrous 1984 campaign IOTL), the NDP could be able to paint themselves as the primary alternative to the PCs.