In those cases you would imagine the party putting a higher priority on consumables and spells that fix the problem.
Unless, of course, you play in the equivalent of a pick-up group, where the spellcasters are perfectly content "their" men-at-arms can't steal their thunder.
Since most fights are sufficiently easy, the full damage output of the fighters aren't needed, only their damage-absorbing quality of being there.
As an added bonus (for this hypothetical spellcaster), his or her disproportionate activity justifies taking long rests as often as necessary.
Or so my theory goes...