I don't see any companies planning to definitely do this forever but the reality is that this situation is probably going to persist for at least 12 months and

I don't see any companies planning to definitely do this forever but the reality is that this situation is probably going to persist for at least 12 months and at that point it's better to just treat it as a permanent transition from the employees' perspective. However even with Facebook you can see they're making a lot of decisions that would make the decision easy to reverse. They're still paying rent on all their existing buildings, they're still encouraging people to live in tech hubs via higher salaries.