Although I do agree with you - I think Jose has been very, very fortunate that the fans aren't in the stadium. He and the team would be getting booed regularly with performances like yesterday and the pressure would be intense on Levy to do something. There will need to be a big decision made in the summer.The problem is that all the scenarios in which they don't make Champions League are also scenarios in which the financial situation is pretty dire, which is likely to decrease Levy's appetite to take the financial hit for sacking Mourinho and also decrease the attractiveness of the position to potential new managers, who surely wouldn't be given much of a budget.
If things get really bad, he will be gone because there isn't any choice. But I think there are definitely some intermediate range outcomes where there is no CL football but he keeps his job because the alternatives just aren't very appealing and inertia is strong.