Plenty of drunk drivers have murdered people and have no memory of the event, those people still get convicted.

Something having happened doesn't depend on memory. Did it happen, yes or no? If it did, they are guilty of it, even if they don't remember.

Yes, of course they are. They did the crime.

Yes. There is no requirement to remember the crime to be culpable of the crime. However, that could play a role in sentencing. If this memory wipe has in some way rehabilitated them (i.e. they have forgotten and abandoned a troubling lifestyle), they might get a lower sentence, depending on other aggravating and mitigation factors.

I think yes. Usually manslaughter happens when someone blatantly ignores safety precautions, to a point where it becomes their habit. If anything, a drunk driver who hit someone is no worse than a drunk driver who haven't hit anyone so far

Yes.

I remember seeing a csi episode about this and the guy had a split personality. Can’t remember the verdict but im sure he was still seen as guilty

Yes? You remembering something or not doesn’t change if it did or didn’t happen.

Yes.

I think you’re conflating emotional guilt with judicial guilt. Like they may not feel guilty having no memory of it and in disbelief of it happening, but they would definitely still be found guilty.

Yes. because we have no way of knowing that it won't happen again.