Each contract is individual, but generally, endorsement contracts have a lot of termination clauses, so Bose could and will end the deal soon, unless Urschel's brand is so unique (MIT math PhD and NFL player? Nothing like it) that they decide to keep him on.
I think MIT math PhD former NFL Player has just as much marketing power as MIT math PhD backup center. So I could see Bose keeping it for a year. He probably has more star power announcing his retirement than all of his NFL career so far.
