VWs get a new spawn option - void respawn
When choosing this option the VW respawns in the world with the "immaterial" status effect, potentially with a timer, say 12h? (This should NOT trigger on a DO res).
This status effect causes most or all other entities to treat the VW as if it doesn't exist (can't be seen, attacked etc.). Possible exception here for demon tracker which maybe gives a special message that there is a faint/wispy presence indicating that there is a nearby immaterial VW.
If the VW does any action that would normally break invisibility they lose the effect and become part of the world again. (Or maybe if they do any action other than move in a cardinal direction and whisper?). Depends on how mad people would be if a VW snuck into your SH while it's down or the ward is down.