With the new emergency QB3 rule allowing that guy to be "rostered" while not on the 53-man roster means they have zero reason to cut Zach.
If they cut him it would mean somebody else could pick him up and pay him league minimum while the Bronco's would owe the balance. If they're going to pay Zach, he might as well be their QB3.
But I have no doubt that the Broncos will be listening to any trade offers that may come their way.