My sole experience with a diverted flight was nothing like this...what seems to be a nightmare. We were over the Atlantic on a DOH-MIA flight when the decision was made to make the 2 hour trip back to MAD. Within 15 minutes of arrival the power of ones passport revealed itself as those able to enter Spain without a visa were invited to disembark. My younger self with an unworthy passport would have been consigned to uncertainty, probably stuck to the airport.
Having traversed T4S to T4 at Madrid, we found buses waiting for us. An hour after landing we were in line at the hotel for check in and in a room shortly after. dinner and breakfast were provided. Information via the app or email was scarce, but reception suggested a noon departure the next day. Sure enough buses collected at us and at MAD the re-scheduled flight had its own chaotic line. I used my gold status to get checked in but there was no time to use the lounge. Ultimately the flight took off well after the re-scheduled time.