In Japanese rules, the hypothetical play to determine life and death is only hypothetical and used only to determine life and death, but then the board is restored to the final position (after the initial passing) for the purposes of counting.
However, there also a lot of other complexities in figuring out life and death, dealing with kos, sekis, etc. I really don’t think the Japanese rules can be easily adapted to multiplayer, simultaneous action games.
This concept is called “pass stones” and is not used in the Japanese rules. It’s actually a feature of the AGA rules, which is an area scoring rules set. Pass stones are effectively a bookkeeping measure that allows one to get the area score via territory counting mechanics.
One could similarly adopt pass stones into Diplomatic Go, by counting each pass (or move that fails due to three collisions) as a negative point, and also counting captured stones as negative points for the player that was captured, but this is just effectively the same thing as the area score.