I've heard about a startup that had to relocate to London after the YC 3 month phase and then wait a substantial time for the INS to work out their papers. That sounds like it could break a company?
I suspect that's the norm rather than the exception. And as such, it can be planned for. It'll certainly slow your expansion (hiring people is hard when you don't know where you'll be located N months from now) but it shouldn't break the company.