Does killing persist if you revert a save?

So, I saw something that said if you kill a certain character:

Toriel

and reset before saving, you'd still not be blocked off from any endings in the game, including the true pacifist ending, even if Flowey calls you out on it.

I'd really like clarification if this is true or not, and if I have to use the special method to actually delete the memory to see the best ending.