Not that uncommon, some places will seat right up to park closing time in each of the parks.
Busses run for a couple of hours until everyone is cleared out, even though they say the busses "officially" run for an hour after closing time. You might have a longer wait for a bus since the crowds are gone and it's not a high priority bus route after the park closing crowds are done, but you'll get back to your resort. Disney knows the restaurant is open, you won't be stranded unless you eat really really really slow.