The cow just went dry. This not an afternoon soap. Change the lead, lose the audience.
Maybe. Maybe not.
If well written, it should be OK. And that show is all about the writing, NOT Sheen. His "Tour" pretty much proved that.
I think the writing is SO sharp they'll be OK.
I also think "killing him off" as a result of his "funny" antics would be very fitting (and funny) actually. Not mean at all, in fact pretty clever. It's not like ANYONE doesn't know what happened here. So, to "finish him off" and enter Kutcher with his new character would work.
If they have the same writers, it's gonna be just fine. IMO