As I understand it, Matty is an institution. A cult of personality. There is literally no way to replace him; people listen to Kiss
because it's Matty. And because they've listened to Matty specifically, for decades, it's become a habit. When he leaves, by definition whoever replaces him won't be part of the habit because that person will be new. The day after Matty's last day will likely see a sharp drop in Kiss's ratings no matter who takes over the chair.
(co-hosts don't really count; they don't listen for the co-host, they listen for Matty)
That said, I think Matty will be there as long as he gets good ratings (and, presumably, that translates into solid ad revenue). I would have to think that given the lofty heights Matty has occupied so long, that when he leaves things will drop so hard no matter what CC does that they have every incentive to keep him around as long as the ratings are good. I mean, I can imagine a
Weekend at Bernie's situation happening.
OTOH, if the ratings plunged this year, I imagine Matty would be gone the next. There's no reason to get rid of him as long as things work, but there'll be a huge incentive to replace him quickly when/if they don't work.