He knows that the devils who are eaten by the chainsaw man will dissappear. By this concept he is doing... Well, the vore thing. What I feel is going to be the catch is that he's eating her like Denji, not transformed into the chainsaw man. So my idea of how this thing is gonna end will be ambiguous, in the sense that you won't be able to tell if the one controlling the "Denji body" is himself, Makima or a mixture of both.
I would be annoyed by an end like that, but based on the previous works of the mangaka, I kind of get the hint that this will end sort of like that or tragically.