Assuming he's not employed by UT, he's likely turned in his keys, etc and cleaned out his desk.
I'd assume he can get in the building. He should have a "legacy pass" out of respect from the Athletics Dept but I wouldn't be one but surprised if his old office is already rekeyed. Pretty standard, at least where I've worked, that when you're done you get "courtesy" access but no real access.
After all, any previous coach is likely a coach elsewhere tomorrow. Do we want to let Graham wander around offices now?