Broken 101,
Difficult questions to answer without knowing the details of the fibula fracture (Weber class??? etc) and subsequent hardware used in the ORIF. Given that it was a dislocation (and 2/12 non-weight bearing) I am assuming that it was a nasty possibly comminuted fracture, with loss of mortise structure and needed multiple screws or k-wire and most likely included an articular (for distal tib-fib joint) fixation screw. Based on these assumptions I would doubt that the surgeon would recommend returning to mixed martial arts (at all) but I would expect a return to moutain bike riding within 6 months all things being well. If it was a simple fibula avulsion fracture with one screw and no articular fixation then I thin kyou would return to both.
Unfortunately many complicated ankle fractures never reach 100% again, however they generally allow return to most sporting ventures within 9-12 months. You have the advantage of youth on your side.