Sorry to hear mate. One of the most common injuries in our sport probably equal to broken collarbone.
I did a grade 3 in one shoulder. Didn't think it was anything more than a sprain until 2 days later the swelling had gone down from icing and I noticed the bump. GP got me to xray and he misdiagnosed it as a grade 1 which I doubted and went for a second opinion. A Physio confirmed later that day it was a grade 3 and put me in a sling for the next few days.
About a week later I saw an orthopaedic surgeon who specialised in shoulders, and said my best prospect was to avoid surgery and do lots of physio. He wouldn't recommend surgery for anything that was Grade 3 and below unless I was a labourer, did a lot of work with my arms overhead, or a professional athlete.
So the next 8 weeks was weekly visits to the physio, lots of Theraband boring as hell exercises. I followed the program to the word and also maintained my fitness by setting up my road bike on the indoor trainer.
At week 10 I had reasonable mobility and strength so the physio gave me the option to do this race I'd signed up for much earlier. It would be totally at my risk.
Decided to go for a light and easy local ride the day before the race weekend and it felt WEIRD. I was wearing a shoulder support brace but the joint had hardly any strength. Could you imagine trying to push your hand away from you and your chest just collapsing forward?
Finished the 2 days of racing with no mishaps but obviously didn't take a lot of the risks I normally would, and was just happy to have finished. I wore the shoulder brace on every ride for probably another 8 weeks during which I continued doing physio.
That was almost 4 years ago.
Since then I have continued riding regularly, focused a lot on skills building and am now able to take much bigger risks. Also done a grade 2 in my other shoulder! If I carry heavy things for a long time my shoulders get tired easily as there is nothing supporting the collarbone but my muscles which are now working overtime. I cannot do pullups anymore, and pushups are risky. No more benchpress at all. Shoulders click sometimes. I have to regularly stretch, do mobility exercises, and rub knots out of my shoulder and back muscles. Foam rollers, pressure point balls, and Theracanes will be your best friends.
Other than that I have full mobility in my shoulders, and almost as good strength as I used to, because I have been able to adapt many other exercises to suit, i.e. shoulder presses, kettlebell swings, rows, deadlifts, using a medium weight.
When I get older I will likely have arthritis in my shoulders. But I don't regret the path that was taken as I avoided the potential risks, and costs of surgery which also has a much longer recovery time. Having the injury and being off the MTB for 10 weeks gave a lot of time to reflect on things.