After looking at the news I now think you are right and that they won't bother with the transition tag. That leaves either sign him to a long term deal, or franchise him.
The problem is that he won't just sign a long term deal, because he wants maximum negotiating leverage, and that means taking offers from other teams once FA commences. That practically guarantees they have to franchise him, then try and negotiate a deal. He would take that deal assuming that it was for around $30m a year since that's what he'd get in FA.
But, even if he does become a FA, about 10 teams, many of them with more money than the Broncos will be in a bidding war for him. The odds he comes here are very low.
In fact, unless the Broncos sign Teddy Bridgewater or Case Keenum, I'd say they are looking at signing Sam Bradford and drafting a rookie.
That would not be great, but it's probably the best they can do without breaking the bank and dumping a bunch of salary (beyond losing Talib and CJ Anderson, whose twitter rant about the Broncos firing his running backs coach indicates he probably doesn't think he's coming back). They might fire all the discontented players and dump Sanders too.
You don't go on social media and criticize your bosses and not have any consequences and those guys have (in Talib's case of course it's his salary that is the problem since they have Roby who is younger and cheaper whom they need to re-sign). The defensive backs all criticized the firing of TJ Ward in not very diplomatic terms. And the negativity just escalated from there.