Supergreen, unless your dh is a surgeon, working nights or maybe in a new job on promotion, he should be able to function easily at work when tired, even if he works long hours.
Ime it is easy to do a senior office-based job when tired, you go into autopilot, can also forget about tiredness by burying self in work, get coffee etc. And is it really likely that tiredness alone would, in most cases, lead to poor performance and dismissal/redundancy?
The health of the stay-at-home parent is as important as that of the wage-earner. Also, if you are tired you could make a mistake that leads to an accident at home or when out and about with the dcs. This has happened to me - near-misses when crossing roads with dd1, falls, hoover falling down stairs, spilled boiling water.
A good test is to look at yourself in the mirror and look at him, and think about how fit and well you each are. If you look great and he looks shattered and keeps getting sick, or is overweight or skinny, maybe it's right to let him lie-in more, but if not then you need to hog that duvet!