Summoning Fury Soldiers against my level 18 Arcanist was delightfully brutal. I like that it is possible to roll certain death. I probably won’t get the exp back anytime soon. Persistence of an instance like that would be a neat benchmarker but I don’t think it will be there after i exit the game. Will the Exp stay put?
Edit: I posted in error (see next post down), so I’m deleting the first part of my post.
Regarding bosses, a fair number of them can seem difficult at first, such as Beholdan. But, you’ll get used to Beholdan and a lot of other bosses fairly quickly and move on to easily beating them, at least when fighting one against one.
There’s always an xp penalty for dying. It’s not particularly significant at low levels (at most a couple hundred xp) but it’s there. You can get some (possibly all…I haven’t read that help tip in a long time) of it back by getting back to where you died and picking up your “grave”.
I don’t believe that your “grave” persists between sessions, and I’m also relatively sure that if you die before getting it back it disappears, but you get a new one where you died the second time, though that initial lost XP is now gone permanently.
Got mauled by a pack of riftspawn not too long ago and in level or two with a few minor item changes for some resists and they all fell relatively easily. Small changes can have big effects it seems.
With the beholdan, any other time i would have just ran but got backed into a dead end. I’m sure if i had time to keep playing i could have recovered it in time. It was exciting and little surprises like that mark a good challenge. Its just a few exp but it was mine. And i bet it has a chance to drop a good eye or something. Never played a game that was so rewarding to play the intro again and a again. I have heroes ready to push on to the later chapters but the beginning is still fun.
Off my own topic, where is a good drop rate list? At what level difference are you just not going to get anything for repeating an area. Part of the compulsion to play again and again is to get the epics. It would be faster with a higher level character but I’m sure at some point its fruitless.
And maybe an explanation of Hero Boss spawns. I know you get better bosses for reputation, but are you going to get better bosses in a low level area with a higher reputation?
You get it all back in Normal/Veteran. You lose a bit of xp permanently upon dying in Elite, and much more when dying in Ultimate.
I remember to have been killed in one shot once by Beholdan’s cousing Mesmer. That was epic. 
You want fun? Try fighting Beholdan and Gaminix while under geared… heh heh heh