People who get on Putin's bad side have a history of ending up with things like polonium and nerve agents inside their bodies, even when living in western countries. Bombing facebook would likely be further than even Russia is willing to go, but I wouldn't put it past them to poison their head of PR or something.
https://en.wikipedia.org/wiki/Poisoning_of_Alexander_Litvine...
https://en.wikipedia.org/wiki/Sergei_Skripal