So, I've never actually seen this happen before, in nearly three years, but it turns out that if an event boss spawns and is not engaged soon enough, the event ends instantly in failure.

So.

Three of us did a zone event in Seratos. Seratos is huge. It was two mages and a cleric, and the cleric didn't have a tank spec set up. So the boss despawned while he was trying to get buttons onto bars.

Now, the thing is, if we had had any way at all to know that this was time-critical, we could have easily gone with "put these three buttons on your bar, and let's go!" and we'd have probably been fine.

But there's no indication whatsoever that you are on a timer for this one. There's no general event timer, there's just objectives, and then suddenly-despawn. No credit at all for the zone event, because the zone event "failed". And I'm pretty sure we'd have won the fight... if we'd had a chance to try it.

Disappointing experience, that.