It would be a real shame if Volotea are not operating scheduled flights from SOU in 2018 and only flying charter flights on behalf of TUI.
With the huge and quite wealthy catchment area of SOU the airport shouldn't have to be in this position every year regarding flights being continued if anything it should be quite the opposite with the airport announcing new airlines and new routes.
In the long term the only hope for SOU is if EasyJet make any considerations into expanding from the airport as the large catchment would easily welcome any move by the airline with passengers having a committed airline to the routes that they want to fly to.