Half his backbenchers wouldn't even support Covid passes so any harsher measures would lead to a massive rebellion.... and he's so weakened now that I can't see how he survives that. He's already on his last chance.
If he does nothing, there's a reasonable chance that things will fall apart completely with health and social care during January, and he'll be blamed for creating the worst national crisis in decades.
The only thing that will get Boris out of this is if Omicron proves to overblown in terms of severity, and there's no big hospitalisation surge. That would probably also require some bold moves regarding reduction in isolation requirements to keep things moving.