It's quite possible that Stobart Air will add frequencies to the DUB route, in addition to the existing daily Flybe 'mainline' DUB-SEN-DUB rotation, when the S15 timetable in released shortly.
The core Flybe flight won't be there for S15 but why they haven't taken it off sale yet is a surprise. It is currently being flown by the aircraft which operates SOU-DUB and they have a nightstop in DUB to provide an early departure to SOU until the end of March, but that disappears and the SOU schedule reverts to its original pre-Southend self.