The ending is just insulting.
"Hey, remember everything that happened in this season? Naaaa, forget it, we'll just start over".

The more impact it will have, the worse it will be.
Arrow finally had something that we can consider a happy ending (if you ignore 10,000 deaths by a nuke), so I don't want any impact on that.

And if the reason is just to find an excuse to shove Supergirl in the same world, that would be worse.
It would practically mean a reset on Supergirl's show too, and for what?
Won't it be better to just say that there is still an existing gate between the worlds so they can meet each others in crossovers using Cisco's vibe, Flash's speed or technobabble from Supergirl's world?
It's not like crossovers are that common even between characters who live just a couple of hours from each other, and that's fine.

So my best case scenario is simply to undo the last 5 minutes somehow and just continue as it should have.