As nobody really knows what transpired on the last meeting between Todt and Hitler, other than it was dramatic and there was shouting, jury is still out on that one.
I think consensus is Todt's death was an accident, but nobody missed him. Least of all, Hitler. There is no evidence pointing to deliberate assassination (I'd call it taking care of him) and it is unlikely that Hitler would feel the need to well, whack him. He could just as easily replace as he did with all the others he did not like. I do not think Speer had the means to kill Todt and besides he was not an obvious choice for replacement.
The fact the accident happened immediately after Todt's conversation with Hitler gives little credibility to the assassination theory. There simply was not enough time to arrange for it if it was spurr of the moment decision.