So on the one hand I am sympathetic here, to this problem, having run a game with a relatively obstinate Maestro D', but on the other hand reading that post leaves me scratching my head, because I sure as hell dropped a bomb in the middle of his opium den the moment things got screwed up.
If the Maestro D' never leaves their establishment, and cares only about their establishment... then that's how you make their life interesting. Through the establishment. It's not your problem that their player is not giving you anything else to work with -- presumably they're doing it because they think their establishment is super-interesting.
If they aren't interested in anything else going on in the world, and they want to hide in their private little bunker-of-life, then the world has to come to them, that's just how it is.
Of course everything doesn't have to be a threat to the establishment -- you can offer opportunities, instead. Opportunities with some cost or trade-off, ideally; opportunities that rely on other PCs or important NPCs to bring to fruition. But inevitably, opportunities gone wrong will become threats as well, and if the only realm the PC ever operates in is their bar, then their bar is going to be where the trouble's at. I wouldn't feel bad about it.
I mean, you say "it would be like if the gunlugger always had problems with her gun", but there's a pretty important difference: gun trouble is boring. Establishment trouble is interesting. A gun is not an environment, a gun does not involved dozens of people in its operation. The number of things that can go wrong with a gun is fairly limited; the number of things that can go wrong with a post-apocalyptic bar are endless.