[Andy]

There was a thread on here some time ago about a foul ball coming from an adjacent field onto your field while a batted ball was being played on. Unfortuneatly, I was unable to find the thread to reference.

The conclusion of that thread was that the umpire shall not call "time" during a live ball, except in the case of severe injury to a player. I don't have the ASA rule reference.

In your case, I can forsee two outcomes.

a) fly ball caught, third out, game over.
b) fly ball not caught, run scores, BR at first with two outs and a tied ball game.

By rule, the umpire cannot call time when the lights went out as a live ball was in play. If the fly ball is not caught, play continues until conclusion.

Let the League director decide how to conclude the game!