I still liked Malack even after all of that. From the looks of the character he just seemed very angry and lonely from losing his children, so when he got to know Durkon, he didn't want to kill him so he turned him into a Vampire so that he might enjoy existence with him forever... Or at least as long as they both could.
Something that bothers me though, is that if the Staff that Malack held had the spell in it, why didn't he just use the staff to cast the spell on Durkon so he would still have the prepared version on himself? Maybe Malack planned for his own eventual demise and wanted an excuse to force Nale to let his guard down after Durkon regains sentience... Highly unlikely, but I can dream, right?
Also, I hope Malack was smart enough to make it be a Runestaff of Protection from Sunlight instead of just a Staff of Protection from Sunlight