Break into his shop and see if he's there. I had a problem with Arcadia staying closed for a week even though she was manning her counter and available as a merchant.
I did and no belethor, he must be dead.
Thanks for the tips bit i'm well aware of the shop bugs, unfortunately this is not 1 of those wait fixes or break in during business hours.
I'm going to pretend he's a werewolf somewhere to deal with my anger of him being gone

I had adrienne die mysteriously in a previous game, inheritance note and all, now belethor is gone...it seems i'm not meant to have all the shopkeeps alive in whiterun, i'm just waiting for adrienne to die mysteriously again and then i'll have to kill everyone in town and never return to whiterun again