Help needed for high level dungeon...

[JonMonster]

I'd be very careful before doing anything that will force the paladin to fight good creatures such as angels etc, some players might enjoy the moral quandry this forces while others will just find it unbalancing and unenjoyable. If you want to still have a heavy combat put devils as the guardians and make the demon a victim of the blood war who was imprisioned here after his defeat or something like that.

There are ways...

Have the guardian be trapped here until 'slain' at which point the guardian returns to its plane of origin or nearest parallel dimension.

The guardian is a creature of honor who recognizes why this combat must be fought. It's nothing personal. You know it and I know it, so, whatever happens, no hard feelings.

Both of these options require a bit of exposition on the part of the Guardian(s) providing a bit of role-play respite in an otherwise combat and trap heavy adventure.

 

[kigmatzomat]

I would recommend a meta-trap that you inform the rogue of through notes or private discussions. By meta-trap, I mean that the entire place is a trap but that the trap isn't designed to keep anyone out but to keep everything in. By that logic, the most powerful traps are at the outside and are "last ditch" kind of affairs that blast the victim back to the heart of the dungeon.

He can disable the barriers and what-not but slowly make him aware that the traps are far more effective from the other side (aka the inside). Maybe have him make some craft:trap rolls and feed him info that way.

This makes him pivotal to the way the party plans to proceed which, IMO, is more important than simply opening doors. A trained monkey can bypass a trap, it takes a true rogue to realize that you might not want to.

 

[JonMonster]

I would recommend a meta-trap that you inform the rogue of through notes or private discussions. By meta-trap, I mean that the entire place is a trap but that the trap isn't designed to keep anyone out but to keep everything in. By that logic, the most powerful traps are at the outside and are "last ditch" kind of affairs that blast the victim back to the heart of the dungeon.

If you go this route you can get away with pulling a huge switcheroo. You have the rogue discover a short cut to the center of the dungeon - first 'trap' they encounter can blast the party to the center of the dungeon and a huge fight with the prisoner. After a huge and epic battle they secure the MacGuffin in record time. They spend a few minutes patting each other on the back before they realize that they now they have to escape from a prison that held a powerful demon for centuries.