The SDCC aren't stupid either IF both teams end up with a game on the same night and Dundalk decide to use the Aviva then the rovers home game would be changed anyway as UEFA don't allow two games in the same city on the same night.
This would cost the SDCC a nights rent from Dundalk and Rovers wouldn't be playing in the stadium that night.
You'd have to imagine that the SDCC will want both clubs playing the games in Tallaght considering the expense they have gone to on upgrades which likely means Rovers will be asked to play away when Dundalk play at home in Tallaght I would guess.
All hypothetical stuff at the moment in any case