This is going to sound absurd and I doubt that show will ever do this since it could ruin the whole premise.
Since time travel was introduced to the universe, the rule has been that any alteration to the past would cause anachronisms and break history; because of this, no one is able to simply go back and prevent tragedies from unfolding, it would be too easy.
However the shows have used the concept of loopholes. Like in the Helen of Troy episode in Legends. Another example would be when Barry traveled back to recruit Captain Cold for his mission, even though in his present he was dead; once he was done, he brought him back to his timeline, thus putting history back in place.
Now there is a way for every death, and I mean pretty much every death in the entire Arrow Multiverse to be exploited in some way, and I'm sure that a lot of people have thought of this already.
And here's my most simple explanation:
That is going back in time, making it seem like that person died to the public eye, and keeping that person hidden until the time is right to re-introduce them.
I'll use this example; Laurel's death. On April 6 2016 at 11:59PM, Laurel Lance was recorded to have died. We all saw it happen, there's no way around it. Except there could be.
The Legends could in turn go back to that specific time, grab the real Laurel, and replace her with a fake one using future technology. Keep her hidden and believed to be dead until a specific point in the future. As of the recent episodes, Laurel Lance is believed to be dead, so all they'd have to do is re-introduce her later on, when the coast is clear as to not affect history. Thus they'd be creating their very own loophole.
I could be very wrong about this, but again even if it's possible, they might never use it, or they could use it once and that's it.
Another thing I thought about was the issue with Barry seeing Savitar kill Iris in the future, around the time the episode aired. I believe that this could've been avoided if they decided to fake it.
Barry could've seen what he thought to be Iris and Savitar (escaped from the speedforce). So what they could've agreed upon is: On May 23rd 2017, we'll make a hologram sequence (like Reverse Flash did in season 1) and make it look like Savitar escaped and kills Iris to your past self.
It's possible, but not probable.