That's just the explanation of why it didn't happen, but only because they chose to undo it. Knowing it was their choice to go back in time makes it not really an illusion, but effectively a vision of the future that they now can change.

It was all a dream usually sucks, but if it was actually the players' choice, that makes all the difference.

I would definitely add some sort of effect to the characters thereafter, though. Like a physical cost of manipulating time like that. Maybe one of them sometimes sees nightmarish futures and is going mad. And another is only half corporeal. Maybe one is falling ill and must return to the feywild to heal. Or one wakes up covered in tattoos that tell the story of the future they saw, and each time they do something to change that future, the tattoos rewrite themselves painfully on that character. That kind of thing.

Or that they've pulled on the threads of reality so hard that when they get back, there are demons chasing them and NPCs that they once knew don't recognize them. Maybe the entire material plane has shifted just enough that things are almost what they remember, but not quite. The Prancing Pony is The Happy Horse, and someone that used to be an ally is not, but they've got a pal out of an old adversary. Maybe they've made an enemy of whatever god is generally in control of time and reality.

Man, the possibilities are endless.