If we refine with isotope separation and lose all the gases to the environment, we will at some point permanently contaminate the vacuum on which the process relies. That will happen before the 1% swarm is complete. The numbers are on https://mirrorswarm.com/wiki/index.php/Chemistry
The vacuum is vital for two reasons. It keeps the processing environment dust-free, and it allows the isotope beam to travel accurately without containment.
On the other hand I can think of no way of containing gases.