It was a game in Mexico City. Rivers was real bad...but Mahomes wasn't great either.
Just two years ago..at age 37...he was a Pro Bowler. He could be done...which is why it would be a short deal...but there's also a chance he's not...and the Colts can squeeze 1-2 seasons of top 15 QB play out of him.
IF the Colts sign Rivers...JB will be gone in a trade. That is what is best for both parties...and they will not carry two QBs with $35-40M in cap space tied up. JB likely doesn't have a ton of trade value...but the trading team is only taking on $13M (which isn't a ton in the current QB market)...so he's definitely moveable...even if it requires some creativity.
JB is currently a sunk cost...and whatever dead cap space is ultimately attached to him is just that. But by trading him...you would be freeing up $15-16M in cap space...which can be used to get a better stop gap. So whatever additional cap space (above the $15-16M you saved) is what that new QB costs.