First off, as has been pointed out, a lot of top-50 kids haven't committed yet, and few (if any) of them are going to pick ND. When they go to other schools, the ranking of those schools' classes will improve, and in some cases will put them ahead of ND.
Second, I don't believe for a second if Kelly jumps to the NFL "the class will fall apart". That's bullshit. A quality hire will more than keep the class together. Does anyone believe firing Hoke has hurt Michigan's recruiting one bit?