But I believe this applies only to local Russian flights - refer to Armavia crash, or the Aeroflot Nord one.
Anyway, one feels it's a catch 22 from the beginning, and that's why they were doomed. Return to Warsaw would be a total embarassment for the Polish side, sending them away by Russians on such an occasion could ignite the bilateral relations. Of course, with hindsight we can say that either of these outcomes would be better, but...