If this government lasts the full term, then the Tories still have time to get their act together before 2029.
If Labour tanks the economy (especially if IMF intervention is needed) then I'd think that the Tories may well go up in the polls anyway, so even if that forces a GE, they'd do better than polls suggest at present.
Plus, they'd saying 'don't interrupt your enemy whilst they're making a mistake' holds true here given the pig's ear Labour are making of just about everything right now!