Andor's Trail

is it normal to recieve giant wasp wing after completing the quest "devastated land?

There are six Giant Wasps: only five Giant Wasp wings are needed to complete the quest,(but all six gives a better result) so there can be another Giant Wasp lurking afterwards.

I'm not sure if it stays there indefinitely, but I can remember killing one after completing the quest, just can't remember how long after.

There's no timer on it or anything like that, so it won't go away.