I've never understood why folks think the Enterprise was decommissioned at the end of TUC. The crew was, yes. But the ship? Kirk's final Captain's Log at the end confirms that the ship will go on.
Captain's Log, stardate 9529.1. This is the final cruise of the Starship Enterprise under my command. This ship and her history will shortly become the care of another crew. To them and their posterity will we commit our future. They will continue the voyages we have begun, and journey to all the undiscovered countries, boldly going where no man... where no *one* has gone before.
Sure, he was really talking about the TNG crew and "this ship" was symbolic of the Enterprise's legacy rather than the physical vessel itself...but in-universe the line confirms that the ship would remain in service. It's just that nobody gave a damn about it since it wasn't Kirk's.