This sentence may seem correct:
"When all this happened, if I wasn’t there, he may have gotten away with it."
but standard constructions says that it should be:
"When all this happened, if I wasn’t there, he might have gotten away with it."
Still, these two terms are often (and acceptably) used interchangeably:
"6 Signs That You Might Be Psychic
Signs You May be Psychic
7 Mistakes You Might Make Before Your Job Interview
5 Money Mistakes Even Good Savers May Make
Fans might have to wait weeks before Dodgers games come to their TVs
Apple Fans May Have to Wait Longer for Larger iPhone"
But wait! You should be careful in one specific circumstance.
If the event did not in fact occur, might is always the better choice.
"If JFK had not been assassinated, civil rights legislation might have been delayed.
If the English had defeated the Normans at Hastings, we might have inherited fewer spelling problems."