He did return for a guestie in 1999 which was quite fun.
I remember him being portrayed as a bit of a baddie or a bit ruthless with regards to opening Bonza Burger and taking business away from the Diner, albeit with comical scenarios. Was he a bit too big for his boots? I'd like to watch his return again because I'd probably appreciate it a lot more second time round. But I can hardly remember anyone actually welcoming him back though - other than perhaps Sam surprisingly (after an initial resentment?). I remember they had an interesting conversation about Bobby in the Diner.
Adam would know Irene, Marilyn, Roo and Alf if he was to return. I think he's the type of character who could actually return without any real reason, simply because he lived there in the past. I wonder how he'd be written if he returned now though, considering the current format.
Yes, with Marilyn being in the current show it would be excellent for Adam to return. Agree that it's risky with the current format.