would that be even possible? I thought pretty much anyone working for them is physically located in Russia. Who would want to (or be allowed to) continue working for them if they suddenly were 100% a remote workforce based in RU?

That is unlikely because Yandex has a "Public Interest Fund" (which consists mostly of government-appointed people) that has significant power, including a right to temporarily replace the general director [1].

[1] https://www.reuters.com/article/russia-yandex-governance-idU...

Seems unreasonable is the market where they make all the money. Would be equivalent to declare bankruptcy