Romania might get a visit from Bon Jovi at some point same as Sofia cause Sofia Entertainment is active in recent years and also you got Eventim behind these shows as well.

If there's going to be a show in Balkans next time Bon Jovi come to Europe, it will be either Sofia or Belgrade or even Bucharest again, the show was a commercial success for the band even at the last minute. People would still go to see Bon Jovi, trust me, and Jon's ego would dictate the band's return for a proper performance. It doesn't matter if this one didn't go well, people would still go to see Bon Jovi in Bucharest. Your assumption is a bit off (but not irrelevant) since there were many first time concert goers in Bucharest. So a bad performance can't disqualify a specific country out of a future visit.

There's not a chance for Bon Jovi to ever play in Greece again unless Bon Jovi themselves want to play in Athens. They played in Sofia cause they wanted to as well. These artists are highly paid and when Ministry of Culture ain't providing any funds nor sponsorships occur from different partners of a X promoter then it's tough to take a financial risk like that.

Anyway, that's just it.