Probably a shit ton. I lost a private key containing half a bitcoin myself.
That's not counting all the "lost" coins from scams, ponzis etc. If you count those, then the figure would be giant.
those coins that went to scammer, are probably dumped, so how in the hell they can be considered lost?
the only lost coin are those that are in any way retrievable anymore
but i still think in the future there will be chances to have them back