I think it was more a matter of timing. TB would have had to sit for at least another year at BU salary if he stayed. He took the bird in the hand and the starting job in Carolina rather than wait for Drew to retire.
That was how I saw it. He was ready to get an opportunity to start and the Saints couldn't afford to pay him starter money to be a back up for another year.
It's all moot if Denver isn't willing to deal. The only hang up is that at 4-4 they're mathematically competitive, so trading the starting quarterback would send a message to the team that they're giving up on the season.
But it'll be a shame if it doesn't happen -- in a month the Broncos will be 5-8, and they'll be playing Drew Lock to "see what he has," and by then we'll have all seen enough of the Trevor and Taysom show to be lamenting "what could have been" if we had just a middle of the road quarterback.