These teams would assuredly get kicked out of both domestic and Champs leagues, and FIFA already said any player who is involved would be banned from the World Cup and Euro Cup. I doubt any of the tier 1 stars would risk missing out on the international tourneys, and the remaining players don't have enough clout to generate enough $$ to compensate for the loss of the domestic/Champs leagues. Seems pretty much DOA to me.
I don't know. I'll preface this by saying, if I had to bet on it, it's not happening. Additionally, I hate the idea.
However, I don't think we should underestimate how much power these clubs yield over their respective leagues. Getting kicked out of Champions League is kind of irrelevant, as this would effectively be the "new" Champions League. The respective domestic leagues may be talking a big game at the onset, but they need these clubs. What is the EPL if it loses it's "Big 6"? To me, this is UEFA vs. the Super League. FIFA and the respective leagues are currently standing in solidarity with UEFA, but they don't have as much on the line in standing firm, in my eyes. I think it'll depend on if this alliance stays strong or if you begin to see some fracturing. I also think these clubs are too smart to just put themselves out there like this, only for it to blow up in spectacular fashion almost immediately. I believe we're going to see a real, long term fight.