I think Vitalik said around 100 million, but that was a while ago. I suppose we have to wait until PoS is in place first before we can get close to a definite answer. Total supply isn't the be-all-and-end-all though. I mean, fiat is uncapped so technically has potentially unlimited supply.
My thought that the fixed supply will have determined after the pos casper already implemented, that means about the next year we will see about the casper network will be alive.
The block reward will be decreasing a lot and just keep your ether.