Why he was sure? Since Putin and his circle, contrary to what your propaganda tries to picture, are acting rationally based on the information they have (which may be outdated or incorrect), just as your country, though the means they have are very much inferior to yours. Apparently at some point the perceived risk from Navalny outweighed potential punitive western measures.

Why not just "stay in the west"? And why hadn't Arafat stayed in Tunis and went to the west bank to be then poisoned there by the Mossad? (As the late Uri Avneri claimed)

Closer to the Russian reality, why hadn't Lenin stayed in Switzerland? And what was the end of prince Kurbskiy who tried to oppose Ivan "the terrible" from Poland?