If he got an Alex Smith injury they still would not cut him because even if it took 2 years to come back, like it did for Smith, you would still have to pay him whether he is on your roster or not for that recovery time.
The dead money for cutting him is just so cost prohibitive that they might as well have fully guaranteed the $450 million because it’s the same result.
yeah, not really. Two years, sure, but that leaves like 6-7 years left on the deal. He would get very little, if any, from those 6-7 years. As of today, there's zero dead money left on his deal from 2026-2031, and its a trivial amount of dead money in 2025.
If Mahomes suffered a catastrophic injury today, and couldn't play again he has guaranteed money that covers the next three years, which is for just under $108M in total.
There would be a little over $336M that he would never see. Chiefs wouldn't pay it (unless they felt super generous), and they could theoretically have no dead money beyond 2024 if they didn't want to.
So on a $450M extension, they could not pay up to $336M of that as of today.
I don't know who on Earth told you that Mahomes had anything close to a fully guaranteed contract, but they were way, way, way, way, way, way off, and clearly never looked at the contract or the structure of it.