Ack, I JUST found this thread! I definitely want Louie back!! But I certainly don't want him to come back to "end" his story line. I'd like to know what happened to him, sure, that's definitely a loose end that needs to be tied up, but Louie is a definite stain on Danny's record. Which leads me to believe other members of the Messer family might be as well. And as much as what Louie did for his brother was something of a reformation, old habits die hard, and we know from Danny in season one most people don't usually just walk away from the tanglewood boys. It's not that simple with those guys. Even if Sonny is behind bars I'm sure theres some twisted relation to Sassone or the other tanglewood boys willing to give Louie, and Danny by association, a really hard time.
I want Louie back, because I want to know where he is atm and what he's been up to, but I hope if we get him back it's not gonna be for the last time. He's got such awesome potential as a really wicked antagonist in Danny's life story. Louie needs to stick around.