Good question. I know a few people who are ready and waiting, not sure how long they'll wait, but they've got quite a bit into this "operation" and I'm sure they won't wait forever.
What do you think they can do about it?
Romania does have an extradition treaty with the US. Cyber criminals from Romania have been extradited to the US before so this will not be something unheard of. I would imagine they would notify the FBI of cyber fraud, provide evidence, and then let the chips fall as they may....
http://www.fbi.gov/newyork/press-releases/2013/three-members-of-international-cyber-fraud-ring-extradited-from-romania-to-the-united-states
Edit to add: this is of course assuming that the "they" you are referring to are US nationals.
Why would the FBI take the lead in any investigation?
If US citizens were effected they will.
But surely not the lead. They might investigate and work together with interpol but they already have democracy in Romania, they can handle the case themselves