Eh, I enjoyed slaughtering them a little too much to join them on my main. Spoilers aside, Mannimarco stayed right where I found him, if you know what I mean. Since, canonically, Mannimarco did kill the Vestige and used their soulless body as an undead minion, my sorcerer brutally curbstomped ol' Manny when the confrontation came. It wasn't even a fight, just a sad attempt by that Mer to survive longer than fifteen seconds.
Now, if I made a villainous character who's evil, I'd probably roleplay him as a double-agent for the Cult, with aspirations to supplant The King of Worms, himself. After all, the Cult does fail, and I'd rather be on the winning side.
Now, when the Dark Brotherhood stuff comes in 2016? You'd best believe I'm gonna be all over that.
Naa i gotta agree with benji i usually play as an orc and it just felt right to slam an axe in his face or cleave his followers in two with a big sword like mauloch demands from all orcs