Hopefully the gates don't go to UA.

JetBlue would be good replacement as the airline using the gates. I could see it adding EWR-AUS. And then, some longer flights like PHX and maybe DFW but I guess those two would be less likely but increasing Florida/ Carribean service more likely. I think JetBlue is more focused on BOS, but it does have a inclination to attract NY market travelers, and EWR is a major NYC airport - albeit in NJ.

Other guesses would be the ULCCs. More Spirit. Probably more likely than more JetBlue, although the feel would be like a nice but struggling grocery store closing in your neighborhood and it's filled with a dollar store and discount store.

Maybe Frontier would considering swapping, selling it's LGA slots to Southwest while opening EWR, with DEN ATL and some of the midwest cities that Southwest had service out of EWR.

Indirectly, this might help Southwest's ops at PHL. Loyal Southwest fliers that were split using EWR or PHL, will gravitate back to PHL in some cases.