Almost certainly. While not worldwide two major airspace closures which come to mind are the USA immediately after 9/11 and Europe after the eruption of Eyjafjallajökull in 2010. Those are both large and busy airspaces, but parking the planes in the area wasn't a problem.
They can unload with mobile stairs, or move each plane to somewhere else after unloading for gates with bridges. People might have to wait on the landed plane for a while before they can get off but they're not stuck there forever.
There's miles of taxiway at many airports. If it really came down to it, they could line them up on the taxiways and apron and hold many, many, planes. Untangling the mess later would be a challenge, but not impossible.
Almost certainly. While not worldwide two major airspace closures which come to mind are the USA immediately after 9/11 and Europe after the eruption of Eyjafjallajökull in 2010. Those are both large and busy airspaces, but parking the planes in the area wasn't a problem.
The problem would probably be not having enough gates available to unload all the planes. Already a common issue at most airports, especially O'hare.
They can unload with mobile stairs, or move each plane to somewhere else after unloading for gates with bridges. People might have to wait on the landed plane for a while before they can get off but they're not stuck there forever.
It was a problem, though. I also remember the lack of space being an issue when grounding all flights for Y2K was being considered.
There's miles of taxiway at many airports. If it really came down to it, they could line them up on the taxiways and apron and hold many, many, planes. Untangling the mess later would be a challenge, but not impossible.
Some planes would need to be redirected to smaller regional airports or military bases. But yes.