Obryn
Hero
I'll go ahead and disagree with Umbran here. If you know you're facing a potentially-deadly combat, you should try to take out as many of the opposing forces as you can, right away. Opening with Wail of the Banshee is a great way to start - your players would do the same to them, after all.
(Also, if they don't drop it on round one, given the way high-level 3e parties can mess with a bad guy, they may never get to drop it.)
If there's a surviving cohort they could take over, that's the best option, IMO. Summoned creatures, too - those are a good idea.
I like letting the player take over a BBEG in theory - but in practice, opponents of this high level take a lot of prep work to run properly. You will know what spells and whatnot the guy has; odds are you know what they do, if you went through the SRD and catalogued them all. The player will not have this prep time. (Of course, if the foe is mostly just a thug who hits things hard, ignore everything I just said.
)
-O

If there's a surviving cohort they could take over, that's the best option, IMO. Summoned creatures, too - those are a good idea.
I like letting the player take over a BBEG in theory - but in practice, opponents of this high level take a lot of prep work to run properly. You will know what spells and whatnot the guy has; odds are you know what they do, if you went through the SRD and catalogued them all. The player will not have this prep time. (Of course, if the foe is mostly just a thug who hits things hard, ignore everything I just said.

-O