We’ll be happy to wait until season 6 to see where this secondary villain goes.
However, as Vigilante is not the primary antagonist for this season, it may simply be that there is not enough time to close out the Prometheus story arc and the Vigilante story arc in the remaining eight episodes of season 5.
It’s a little surprising that the audience won’t be finding out exactly who Vigilante is this season, as the show usually deals with any new mystery characters within the same season that they appear.
We do know that next week the Green Arrow and Prometheus are going head to head after the villain kidnaps Oliver’s girlfriend, and with Vigilante no longer targeting Oliver, he will probably remain a background villain for now.