No one was particularly interested in prosecuting John Adams when he was found alive, and he was eventually granted an amnesty. Maybe there would be more reluctance to do this for Fletcher Christian since he was the ringleader, but I suspect that the result would be the same: no one would want to go to the expense of bringing him back to the UK to stand trial for a mutiny twenty years past. Captain Bligh certainly had other issues on his plate at that point and was in no position to be vindictive (and he doesn't appear to have been vengeful toward Adams in any event).