The Flash Season 3 Finale: 8 Big Questions We're Asking After 'Finish Line'
7. Why Didn't Savitar Disappear Immediately?
As mentioned, H.R. changes the timeline when he disguises himself as Iris and dies in her place. As Ms West's death was the catalyst for Savitar's creation in the first place, this means that the God of Speed is now a paradox and can no longer exist. As Team Flash explain, he could disappear at any moment.
But, for some reason, it actually takes the whole rest of the episode. So why is this? Back in season one, another evil speedster was blinked out of existence when Eddie Thawne killed himself, thereby cancelling out his descendant, Eobard Thawne, from the timeline. On that occasion, Thawne disappeared straight away. So why did Savitar get a longer farewell?
I might be clutching at straw here, but maybe it is because the sequence of cause and effect that led to Savitar is more complex. With the Thawnes, it is very clear that Eobard cannot exist without Eddie. With Savitar, however, Iris' death is just one part of the chain - in the original timeline, Barry became darker, which led to him creating time remnants in his fight against Savitar, one of which became Savitar. When Iris' death was taken out of the equation, maybe it just took some time for the changes to history to catch up with him.
Or this is just a massive plot hole and he didn't disappear immediately because the episode had another 35 minutes left? You decide.