In my case it was a connecting Air France flight from Paris to Mumbai that had to turn back to Charles De Gaulle after encountering problems en-route. Half the passengers were Indian nationals with either single-entry/expired Schengen visas (like me) or people passing through from North America or the UK.
The Air France staff wasn't particularly apologetic about it. They did everything that they were supposed to but half-assed it. Everyone who needed transit visas got them but we had to spend 6 very frustrating hours in line with not much communication. They sent sandwiches for passengers waiting in line but vegetarians got left out. The airline put up everyone in a hotel, with shuttles to and from the airport, but I got to the hotel at 3 AM (after waiting in line for a transit visa for so long) and the next flight was the following afternoon, so I couldn't get much sleep.