If you were fighting it while the server crashed it was unleashed, which probably means it despawned. Not entirely optimal, I shall readily agree.
"The psychological trials of dwellers in the last times will be equal to the physical trials of the martyrs. In order to face these trials we must be living in a different world."
I would wager taming is the same for a boar as it is for a aurouch or mouflon, but because it's you know, a BOAR... I would ask someone who can consistently UA boars.