The biggest hurdle is often the check-in desk at the airport. No permit - no boarding. Even if you're from a visa free country they want to see a return ticket. No ticket - no boarding. Since airlines have to pay for your returnflight if you are stopped at the Schengen border, they are very strict about the right papers.Why were you guys worried about travelling with expired permit? As long as you don't exceed the 90/180 Schengen rule, can't you come and go as you like, even without the permit?