The scripting error, in which you speak of, has already been enacted, so no amount of patches will fix it without starting a new play thru. There is only so much a patch can do. It can fix it from happening again, but not from reversing what has already happened. If you have a save from before you left for the Sierra Madre then reloading from that save would probably fix it, but if not.... sorry dude, I'm afraid your current play-thru is borked.
So this is a ridiculous answer, but you don't work for Bethesda so I get what I paid for.
The sad news is, I *DO* have a save from before I left, and I loaded it up...and he still blows me off. Apparently the bug occurs when I go *IN* to the DLC, not when I come out, and I don't have a save from that far back, so I'm just frigging borked and might as well just uninstall the game because I'll be damned if I'm rolling through all that content again because of a bug.
I sent Bethesda a tech-support email...days turned into weeks, no answer of any kind, not even an acknowlegement.
There has *GOT* to be a way to reset Arcade. I'd even accept losing everything he has and having to re-recruit him, since I've not done any of his missions, but this "Hi, I'm wearing the stuff you gave me, and yes I know I'm supposed to go with you, but I can't because you have too many people with you, that being 0."