As a bottom, if i agree ahead of time "don't pull out no matter what," I fully expect to get bred. Guess that is where a safe word would be needed. Otherwise, you don't know where the RP ends and revoked consent begins.
I've not been in the situation, but as a chaser, I know for a fact I've jerked off to fantasies of changing my mind at the last minute and cumming so hard imagining a toxic top breeding me anyway. I don't think you can really fault any top who breeds you as you say no at the last moment, unless you never gave consent to being bred to begin with.
If we agree you won't cum inside BEFORE you are inside, then it is absolutely wrong to cum inside.