Level 10 should be perfectly fine. Sarevok is a pretty straighforward fight, specially after you kill his minions.
He cures himself by dealing damage with his sword. If he he's regenerating a lot of damage and killing chars in a turn that sounds like a build issue. Your front chars aren't build with enough AC and damage reduction to stop him and/or your weak chars are taking innecesary risk and being targeted.
So, take a look at your builds and party set ups. This is one of the easiest boss fight of act III
I can't remember if you can disarm him or not, but examine him. If you can disarm him that would trivalized the fight.
Also, if I remeber correctly he isn't inmune to blind. If you don't mind a "feels like a cheat" tactic just use darkness and a character that can see in magic darkness
He can't be disarmed. I just did that fight again and looked at his stats to see, if Disarming Attack would do something, it doesn't.
OP: get your more squishy party members away from him - there is a kind of balcony on the right side ( if you look at his throne), get Gale and other characters with lower AC and hitpoints up there. I used Distracting Attack with Lae'zel ( battle master manoeuvre) and spells like HoldPerson and Otto's Irresistible Dance to keep him from moving away. I had some summons - my bard had by that time read the Necronomicon ... sorry Necromancy of Thay and had the Danse Macabre summon, plus Us, Jaheira had a fire myrmidon and the woodnymph out, who summoned a Woodward - it was pretty stuffed in there
, but he died pretty quickly.
