1) He discovers that his best market offer, having been a backup for 4 years, is to continue being a (better-paid) backup somewhere else with an aging veteran in front of him who he might see as an injury risk, like in NO, SD or (pukes a little) NYG.Edit: besides backing up Brady for much-more-than-backup money, what are the other scenarios, InstaFace, that a healthy Garoppolo isn't a starter in 2018? Someone will pay him to start, I think.
2) He gets signed as 1 of 2 QB hopefuls to compete for the job, and doesn't decisively win the competition
3) He ends up with a shittily-run team like the 49ers or Browns and is never given the kind of surrounding talent necessary to make a pro bowl
On BBTL, I've got one of the higher opinions of JG's talents, but he's never going to arrive at a new franchise with the same level of heraldry as a new top-drafted QB, and won't be given the same amount of privilege to start soon and won't be given the same amount of rope. Everywhere but Foxborough, the GM and HC have too much ego wrapped up in their top picks - it would be admitting too much failure - to not give them immediate starting roles.