Would be the worst decision on both of their parts for the obvious reasons.
Cotto : Would catch heat for an easy payday low risk / low reward.
Khan : Would be knocked out and his wife would gloat and would be less than irrelevant.
Hindsight is 20/20 lose /lose for both.
It'll be just like the Canelo fight except this time instead of Canelo hitting him with the Right, Cotto will catch him with the hook when Khan jumps in with his chin. Guess if Cotto wants to go out with handing out a knockout for his retirement fight, then this fight makes sense.