The "first wave" left when he first instituted the draft, the second wave left when it became apparent that Russia was losing and the war could drag on for years and economic stagnation was assured.

There's no question Russia is suffering a talent and wealth drain, but that's still estimated to be around 1,000,000 or so out of a total population of around 145,000,000, so less than 1% estimated have fled due to the war. Probably more than that will die or be injured in the war before it's over.