You are crazy. He had really showed his age this year or that he was out of shape... whatever narrative you want to give it is fair... but neither are good.
This is a full year injury... at least. Many guys suck the first year back... so roll forward 18 months and he still is not likely to be at or near his playing level this year. So he's looking at a 2 year process imo... and its effing hard... and it might eat a guy up at his age. It would be a mental and physical battle. I doubt he plays in the NBA again. I think he rehabs and plays in Australia and he likely gets some ownership in the franchise he picks.
My guess is Joe would have had a bench spot on the next Olympic team as a goal for his retirement, along with patty mills and aron baynes. Looks like patty might be the only one to make it. In terms of coming home and buying a team, I dunno. Delly is currently playing for Melbourne United, I believe his deal will likely have an ownership stake attached when he retires, Dante i think owns a slice of South East Melbourne Pheonix, Bogut has a share in the Sydney Kings. The Adelaide 36ers, (team that passed on Joe as a kid pretty much) might make sense but who knows if there will be a share available for him. The league has just expanded into Tasmania so I doubt there will be any expansion in the near future. Melbourne and probably Sydney could support another team, in a few years, there has been a huge influx of local talent coming home from college ball in the US.