While adventurers are always an issue(for every villain) this guy still has ways to deal with them. He has a 17th level cleric for his second in command, and since he is charismatic he can take ranks in social skills and get SOME of the other high level casters in the world on his side. With both his clerical "Dragon" and a bunch of high level casting conspirators/allies, he should have no issue taking out some messily low-mid level adventurers...it's the high level guys he has to worry about, but since he's a BBEG and not a PC I can basically give him access to any resources he needs...so yeah. Of course, as a BBEG the players will, eventually, defeat him....or join him, if they so choose.