Okay, I understand that healing the mercenary involves auras, but without life steal, he still survives?
Also, what's a good base for pride?
Cure/Prayer/Insight combo will keep him alive for the most part. He'll heal up between encounters pretty quickly.
Personally i prefer Might aura with a life leach helm, such as Tals, on my merc.
With Amp Damage from a cursed demon, he still deals enough damage to stay alive quite well, besides against t5Heralds which you can't really stop them from killing your merc if they target him lol. Your Bind Demon is the only thing that can really face tank a powerful Herald.
Good Pride base is just any Elite Eth Polearm. Pride doesn't have ED on the runeword, so you'll want whatever can give you the most damage. Eth CV is good for it and is the cheapest of the elite bases.
Between Might, Concentration, Amp Damage from Cursed, his damage will still be good enough to keep him alive in normal play with some life leach. Can go for Fanaticism Aura + Cursed on your demon to do even more damage. But any of the Holy auras will work great as well, since it'll spread Amp from the Cursed constantly.