Our RP forum rules don't exactly allow for Mega Evolution in a PMD setting. Pokemon Super Mystery Dungeon introduced SOME kind of a roundabout way to access Mega Evolution for a number of turns within one specific dungeon through use of the incredibly rare Awakening Emera and a looplet, but as the odds of running into this sort of thing are pretty phenomenal... Probably for the best not to try.
1) Would it be possible for a Pokemon to Mega Evolve without the need for a trainer, despite no precedent (that I know of.)
2) If it were possible, how should it be treated in a Role Play setting?