Oh man that's awful for Embiid. Like @keevsnick said, if you repair it with surgery, it's 2 months minimum but probably more like 3-5 months realistically. If they decide not to do surgery to repair it, and remove it instead, it might be less than 2 months HOWEVER that could really impact the rest of his career and possibly even cause early arthritis (or chronic knee problems).
Ron Artest did the latter and was never the same. I believe Westbrook underwent the surgery back in 2018 when he had a torn meniscus but he obviously missed significant time. Westbrook is still a great, explosive player now though.
Like others have said though, I think this season is compromised regardless for Embiid. Even if he can return by playoff time, he'd still need to do a lot of rehab/conditioning and probably play limited minutes. No way he'll be 100% healthy again this season at least.