My ACL tore a few years ago when I also broke my leg at the top of the tibia...well to be more accurate, it popped out of my leg bone cuz the piece it attached to got cracked. I sat out the rest of the season. There was a period of a few months after the bone healed, before I knew the condition of my ACL, then I went in for the surgery. Luckily, the bone healed such that the ACL was secure again in its place, although just a tad loose. The Doc said he'd have to do the best replacement of his career to get what I had at that point, so that was it.
For me, it was not worth risking the other structures that become more vulnerable when the ACL is not there, so I didnt so much as ride at all until I got the clear. What Im trying to say is every time it "pops" out, you may be tearing the cartilidge up, and MCL, etc... If the cartilidge on the Femur gets too bashed up, that can lead to big problems down the road.
If you are intent on riding, Id invest HEAVILY in some nice braces for sure!