I GOT HIM !!!!! finally.... GoSac made it possible only 2 or 3 tries and he was down... but all in all I wiped over 50 times and also had soem good tries without GoSac (6% with GoServ and failed because I failed ^^) so its possible without gosac too I think but dispelling without eating the dmg from the felbreath helped a lot
killed him right after he summoned the 2nd doom lord ilvl 501 with destro had about 1 or 2 min left on the curse of doom.
10min CD (doomlord) safed my ass during 2nd fel pup phase as he killed the 3rd pup and I could take back my pit lord who wasnt far enough away so he got dispelled and was running towards me... was close as fuck ^^