Are you sure they can’t be extradited? Rosenstein specifically mentioned that they would be moving forward with extradition proceedings. I don’t think he would say that if there wasn’t a legal basis for it. A better question might be, to what degree does it require the cooperation or consent of the sending country? Plenty of room for more mischief by Putin: he can resist the extradition and have the Dems jumping like jackals (RUSSIANS PROTECTING TRUMP!!!!!) or he can put the screws to President Trump by handing them over all while saying: “see what a good member of the family of nations we are”
They were working for the Russian government. Nyet...
Any country can REQUEST extradition of any suspect(s) or indicted person(s) from another country.
Without a standing extradition treaty (which does not exist between Russia and the USA) it is highly unlikely that any Russian national(s) would ever be extradited from Russia to the USA. They won’t even let us have Snowden, a US national. But Putin could decide to extradite anyone requested, if he thought it was in his political interests.
The US can request it but Russia will surely deny the request.