I had a skeleton surprise at one of my bases and portaled out in the middle of it. It stayed active there for quite some time, but eventually I ended up getting another event somewhere else. When I returned, there were still skeletons there, but the event was over.

I don't know what caused it to end, but it did eventually end, although It did stop the raids for a while at least.

Yeah, the one event that my friend triggered actually stayed active for over 9 hours but that was with no one logged into the server. Which from what we can determine, when there is no one on a server the game effectively 'pauses' after a couple of minutes with no activity.

i once had earth is shaking (troll attack) followed immediately by stench from the swamp (skeleton&draugr attack)
but never had i encountered event at the same time as my teammates.

it's an interesting find though. thanks for the tip!

You have to kill the enemies when the raid event happens, if you dont kill the enemies; it continues until thy is done.
We have never had so far multiple raids simultaneously. Not sure if that's a thing, I hope not. You can have raid after raid in short time but at the same time don't believe so.

I also believe the raid has some sort of "maximum" time limit where it force shuts down if the raid is not completed or the enemies are not able to destroy anything anymore.

raids are on a timer, you just need to spend time in the zone, any leftover mobs will poof if you run them out of the zone