I'm playing with OOO, but I'm sure even in vanilla oblivion you'll encounter this:
I was wandering somewhere and found a fort. I enter, then I find a room with 4 marauders plus a warlord. How will you even survive that assault?
If you'r a warrior, sure you can tank, but a 5 marauder attack will be hard, with them holding warhammers and axes.
Depends on the warrior. I've roleplayed a couple of them not to use magic (except Restoration). I play Dead is Dead in the vanilla game. Minors as majors (so leveling is kept in check) but I never touch the difficulty slider. I've had a couple of fighters die over the years. They just get overwhelmed.
My longest-living warrior-type character (Dyan phor a Cauz, the paladin) uses A LOT of detect life and sheild spells. She's got dozens of detect life and sheild rings, too. She generally does okay against multiple enemies. If not, she runs. As a paladin, I also roleplay her Restoration abilities to be as good as she can afford. She usually has a litany of healing, invisibility, & fortify potions at all times. If she's out of potions (note this) she does NOT go dungeon-diving, unless the area she's going in is known to be stocked with a bunch of weaklings like imps or low-level undead.
If your a mage not adept at casting illusion spells, you're in even bigger trouble, unless you can one shot everything.
When both my mage characters were not adept at higher illusion spells like Invisibility and Command, they'd simply avoid such a scenario. We'll get 'em next time. Or they'd hide themself somewhere and conjure a zombie. Zombies can take a lot of abuse for their masters.

If your a thief, then you'r going to have a hard time at them not detecting you while poisons do the work.
Both of my thief chars are/were terrible fighters. They generally don't go into subterranean dwellings much. There's plenty for them to do in the game above ground; stealing loot and such. They always wind up with this huge amount of money for what amounts to very little work. "Who would want to go in an Ayleid ruin with traps and all sorts of monsters, when it's so much easier to rob a sleeping noble?" my thieves rationalize.
What do you even do? Drink all healing potions you have?
btw, I get past that kind of situation with a frenzy spell, and I think that's the only way you beat mobs.
That's funny, I've never ever used Frenzy. I have no idea what it does, actually. :guilty: