I think this is the beginning of Savitar, so they couldn't possibly alter it without altering their own pasts.
From what we've seen I'm convinced that Iris death is set in stone and nothing will change it, because I am convinced that the Savitar that we see killing Iris is the youngest version of him, who has only just become Savitar and has yet to be imprisoned in the Speed Force so if Barry did manage to stop him then he'll be undoing his future actions which is the past to them, and the timeline will be screwed up even more than it is. Then after Savitar kills Iris Barry will create the prison that traps the younger Savitar before defeating his present day counterpart, which Abra Kadabra confirmed does happen, but will be left to mourn Iris' death. That said I think I figured out how Iris could be saved without interfering with Savitar's actions and leaving his past intact while changing the future back to how it should be.
Barry could remove Iris from the timeline and place her a few months ahead of her own death, like what Barry did to Eobard.
When Barry created Flashpoint he had Eobard Thawne imprisoned for months but when he released him so he could kill Nora again, Eobard became a time remnant who survived his fate while his previous actions remained intact and furthermore he retained his memories of his previous life. I think Barry can do something similar with Iris after watching her die by going back and removing her from the timeline and jumping her ahead several months, and through Speed Force paradoxes Barry basically makes Iris a time remnant. That way her death remains intact to everyone else and she'll probably remember it also but she'll never have physically lived through it herself, and the future changes back to how it should be with Iris writing about the crisis in 2024. I think this is also more possible if Barry is going into the future to talk to 2024-Barry and he learns when Savitar is defeated so he knows when to bring Iris to.
I'm like 95% convinced that the Black Flash is coming for Barry when the season ends.
However the biggest problem is that the Speed Force itself has warned Barry about his recklessness and told him that it won't stand for him changing time yet again after Flashpoint, much less create time remnants. So if Barry does go back and save Iris then he'll likely get the Black Flash sent after him and chances are he'll probably die instead. I have actually been convinced of this for a while now as it is completely within Barry's character to rupture time and space to save those he loves, a sentiment we've seen the Speed Force doesn't tolerate. As I've stated in a previous post I think if Barry does die like I think he will Season 4 would be a good time to adapt the storyline The Return of Barry Allen from the comics for the first half of the season. Obviously if Barry dies it won't be forever but I think it would be a good change of pace if he is gone for a while, and the team tries to adjust to fighting crime without him as Wally would most likely stand-in for Barry. I don't think that means Wally would become the main character but rather the show would focus on each character equally like Legends of Tomorrow does, until Barry makes his return.