>> otherwise he wouldn't have used Novichok.

The whole point of using biological weapons like these is that it's almost impossible to prove that poisoning actually took a place. No one would ever find out for sure if he would die and only reason he still alive is few lucky conditions.

In his earlier investigation video Navalny himself told about two previous cases where he and his wife was likely almost killed, but they never suppose it was poisoning since it's impossible to understand it unless you actually dying. Only now they found out that the same FSB agents followed them on the trips earlier where they became sick with no reason.