Time. Give him all the time.
The main lesson I took away from the Greg Oden debacle was Portland's complete mishandling of that entire ordeal. There should be no pressure on Embiid to return, contrasting how it was with Oden. Get Joel 100 percent healthy. Then I think it would be best to give him another 40-60 days after full health to get in the best cardiac shape possible. Not muscle/weight as a priority, cardio. People underestimate how important being able to exert yourself is. Muscle is important in the long, long run. Being able to stay on the court for 27 to 34 minutes a night is most important in the now.
Oden's added bulk after injury made him more foul AND injury prone. Those two things keep you off the court, preventing the highest quality learning and adjusting period to start a career and jeopardizing your prime due to possible injury recurrence.
Just give him time. MCW's second year, the debut of Nerlens Noel, and the addition of KJ McDaniels will more than tide you over until whenever Embiid returns to action at 100%.
Yes, even if it takes the entire season.