They'll bitch and moan then their finance manager will tell them to pay up because it's worth it. At least how I see it going down. Having that type of reach to your audience is pretty priceless and Twitter is the best means for quick short form messages to everyone that can be shared easily. Instagram and Facebook don't let them hit their followers in quite the same way.

Alt services don't stand a chance due to network effect Elon would have to really piss off everyone if it's just a few they can't really move effectively plus Parlor and those don't have the servers for massive amounts of people I don't think