A majority of the supposed guarantees you see advertised in contracts these days are susceptible to a guy getting cut. Its the downside of the famous "injury guarantee". Many of the bonuses are susceptible to injury (hard to get game day bonuses if you are on IR, good luck with Luck cashing in on Pro Bowl or MVP money).
If Luck is let go next year because his shoulder is shot, he will lose a substantial portion of his "guarantees" and "bonuses".
The only thing guaranteed is up front money. Teams would prefer not to pay it that way. Its really all you need to know.