Taking an enemy capital while yours is enemy held results in the destruction of money… the raided IPC’s can’t be claimed, they just leave the game.
So, in the example above, Japan can still help the axis by destroying Russia’s income, but Japan is still zero income, zero dollars.
Oh, interesting House Rule from an era long past…
Capital Relocation…
If your original capital is captured, and you are in control of an enemy capital, you can re-locate your government to the former enemy capital. you still lose all of your money when your original capital is sacked, and you obviously will not have money to purchase on your next turn. But, at teh end of the next turn, your government has settled in to their new headquarters and collects any income from territories they still control, and continue from the former enemy capital…