Whatever the people who did die would go on to do in their futures now won’t happen, and even the smallest tweaks to the timeline can have lasting effects.
(Seriously, Barry and Iris, send Nora back to the future before a point of no return.)
The differences between Cicada’s victims could have far-reaching consequences.
Nora stated that Gridlock and one other didn’t die in her original timeline, so their deaths in the changed timeline means everything they did in the rest of their lives no longer happens.