This was always going to be a question and the same reason Aiden McGeady didn't go back to Celtic this past window. If Tim Howard is unwilling to drop his wage demands then there is no way he's going to end up playing back in MLS. He's got name recognition and should have plenty of reason to get paid well back in the United States, but he's not going to make what he would have made at Everton next season.
There is rumors that he also wants his next deal to go for 4 seasons, which has to scare MLS teams looking at him going till he's 40 years old at good money. If he sticks to his guns then it's highly possible this MLS switch falls apart before it even gets close.
What does Everton do if Howard won't move back to MLS this summer? That's the million dollar question. They might try to sell to another Premier League side looking to take a shot that Howard can still play like his World Cup days, but he can also fail to take that move as well. Hopefully the lack of playing time here as Joel Robles has overtaken him really makes him take the chance to leave and not drag out the ordeal.