Try not to freak out, as he could have just had this one incident, and after the meds and rest he may fine and with some exercise those ligaments can get stronger and tighter.
Alot of us are using Cosequin as a joint supplement
The company name is Nuxtramax and apparently they have actual case studies of improvement from this product. So I would start him on that.
Now as far as surgery goes....There are 4 grades of LP (4 being the worst, its when the patella is in a permanent out position). IMO Grade 3 and Grade 4 should have surgery to correct the luxation. LP can't get better on its own. My advice is to seek a consult with a Board Cert. Ortho Specialist. A lot of general Vets attempt to do this surgery, but honestly, it is a major surgery and you want someone with the experience, knowledge, skill and most of the proper judgement on how to repair the damage once they are inside for surgery.
I can recommend a Specialist but we on Long Island, not sure where you are?