Well, one of the most commercially successful blues-rock albums of all time is ZZ Top's Eliminator, which was all done with 8 bit drum machine samples in the 80s, before they had things like humanize functions and velocity layers and room mic samples, etc etc. So the idea that you have to have a real drummer to be commercially successful or "CD quality" is nonsense. That said, a human playing a real drum set can bring a certain something extra. So really, it's up to you and whether you think he can add something. Maybe you should just try recording him for the *next* song and see how that comes out, see how it compares to the previous recordings and whether they sound out of place now alongside it.