I tend to disagree the character was in play. Its just revealed, and then discarded/eliminated. The card itself creates the attack, and it never mentions the card is in play/set aside so I assume its technically in your hand during the resolve of Ride Against The Enemy.

I would add a sort of clausule that they remain playable at their homesite: V] Lost in [the] Wilderness/Border-lands/Shadow-lands Hazard long event Non-avatar characters may not be brought into play at any non-haven site that has a [W/B/S] in its site path, unless its their home-site. . May not be d...

Is there a limit on which cards to use? Are there certain cards that probably will never be virtualised?

I think Mark did the right thing. I will not take sides in the conflict whatsoever, I just remember a Dutch proverb: "Where two argue are two to blame."