If Rubio drops out, he will not be able to compete in a brokered convention.
I doubt that anyone else will get out.
He’s leaving the senate, so he did not like that. The only way to embellish his credentials would be a governorship, a cabinet post, or the VP slot.
Like you say, he’s not going to get the nod if there is a brokered convention.
So a brokered convention can consider someone new but not one who has already withdrawn? Didn’t know that