I don't believe the future is set. I refuse to believe we are all destined for a particular fate and we are all locked on course until we reach our destiny. As Yoda said, "Always in motion, is the future!"

The course of our future could be altered by an infinite number of decisions we make over the course of our lives.

What Barry saw was one possible future. It's not written in stone and can be altered by any number of factors, actions, decisions, etc. Which is pretty much the entire point of the story arc: how Barry changes that future event where someone could die.

If you believe in a circular universe, or cyclical time line, then everything happened originally... once. After that, a cynic could argue the universe is just repeating itself and nothing is new. A philosopher could argue it's just the same, original universe, reiterating itself, and therefore it's all new EVERY TIME, for who lives who can argue otherwise?

... Meanwhile, in comics world where people can time travel and witness events unfold outside of their natural, linear flow, anybody can muck around with history.

I have always wondered that myself. I hope he can save Cisco from losing his hands with that fight between him and Killer Frost aka Caitlin.