That may be part of the calculus but I think its mainly a desperate threat being bandied around in the heat of the moment, rather than part of any kind of well-considered strategy.It's an attempt to align the players against ESL. Players are going to be very wary (a salary cap is the obvious move for ESL once they lock in never worrying about relegation). Basically UEFA says... play on ESL and you can't play in the Euros of WC, with the hope players say.... "my contract doesn't cover ESL, and I won't sign one to play there if it costs me international play", with the threat to follow being that if the clubs are really banned by their leagues, the players can request (and likely get in most countries) release from their contract.
He's basically making the (likely empty) threat that if you go to ESL as a club, the best players will desert you for no compensation. So you have your big name, but 2nd and 3rd tier players, while the top players move to the big money clubs left behind. Also interesting... if that happened, big money would be lining up to invest in the West Ham and Newcastles of the world.
I think the reality is that this change, if it happens, would probably benefit players on the ESL clubs, at least from a purely financial standpoint. There is going to be a massive influx of revenue to those clubs, there will be competition between them for players, and the players are going to reap benefits from that in their wages and other compensation.
If UEFA really does try to ban ESL players from participating in international competition, I think you're more likely to see protests and lawsuits from the players against UEFA than an exodus from the ESL clubs.