It will probably have been in vain. Southampton clearly been cheating. Clubs get thrown out of cup competitions for inadvertently fielding an ineligible player, so I can’t see how they don’t get thrown out of the playoffs for spying.
But it’s completely unsatisfactory for the result to be determined in a committee room, rather than on the pitch, whichever way the decision goes. If it was up to me, I would order the game to be replayed - possibly with Boro having a one-goal start.