Depriving Russia of nuclear scientists, or capable people in general, might well be worth whatever wages they brought home.
If you want to bring the inter-european war into it I’m not sure if we can afford to be unpragmatic about this. By all accounts letting Russia bleed manpower in exchange for some small wages is well worth it. If you want to deprive them of money you really need to strike at their ability to export gas and oil at inflated prices. Advancing knowledge about fusion aids that goal, though the effects are likely (hopefully?) too late to matter.
Well, who did you trust to build your hardware?