I'm assuming the answer is going to be "First player chooses" but it doesn't hurt to make sure ... :-)

A timing question that occured in a game yesterday ...

Leo Anderson was sitting there with his Personal Story un-finished. The Loss condition reads: "If an Investigator is devoured, or the Terror Level reaches 4, place Leo's Guilt in play." Leo's Guilt reads: "If Leo discards an Ally, he is devoured instead."

Leo's starting ally was Earl Sawyer, whose text contains the line: "Discard Earl Sawyer if the Ancient One wakes up."

Diana is then Lost In Time And Space and at the end of that very turn, the Ancient One wakes up. So now, adding it all together, one of two things happens:

1) Diana is devoured and Leo loses his story. Leo discards Earl Sawyer. Leo is devoured.

OR

2) Leo discards Earl Sawyer. Diana is devoured and Leo loses his story. Leo is not devoured.

Which is it?

I personally resolve similar timing issues in favor of the investigators, whenever possible. You are correct in your assumption. I believe it is up to the players/first player to decide the result of such simultaneous matters.

There's no reason to think they aren't simultaneous, and since they're simultaneous, you should be able to chose the order they're resolved (in my opinion). FFG seems to rule that way anyways. (Take the question of passing and failing a personal story simultaneously for instance).

LiTaS devourings occur while the AO awakens. I'd say it's simultaneous, and therefore the players' choice.

I would say it all depends on the order of play. If Diane goes before Leo, Leo is devoured. If Leo goes before Diane, Leo is not devoured. Why abandon the order of play when it clearly resolves the matter?

Red Bart said:

Because there's no precedent for dealing with any timing issues in that way, except for phase order (which it was designed for).

It clearly does not resolve the matter.