This is a basic jurisdictional question. If Atos has "minimum contacts" (term of art) with the United States, then SFOR can sue them for damages caused by Gelmato, presuming they end up completing the acquisition. Any first year law student should be able to establish jurisdiction over an international company like Atos (both personal and federal subject-matter jurisdiction).

For those with the time to read it, here's a decent article on personal jurisdiction. https://civilprocedure.uslegal.com/jurisdicti...al-courts/