It's not just the ~300 days in prison. It's not like it was hard to kill him at any point prior. Not to mention the dumb fuck did more to die himself with that "poisoning"(probably an OD).

Honestly, I don't see a single reason why Putin would do it. The situation was perfect for him as it was - Navalny was largely forgotten and had no bearing on anything. If anything, he won't appreciate a minor shitstorm on the Internet a month before the elections.

But hey, "great" people can't just die of health issues, it's always someone!