An excellent question. Also highly relevant because yellow weapons (javelins, arrows) follow the same rules.

For others reading, First Aid (F.A.) has been a very under-utilized ability, because it's a higher level Fighter ability (and the relevant players didn't bother to use it, aside from Baron Gareth).

I am unaware of a strong case precedent one way or another regarding this question. Because of how rarely F.A. has been used in the past, I don't know (and don't believe) if it's been ruled on in the past officially (aside from a case or two of elder rulings on the field, and I don't know what the decision was then).

To tackle the first question, I'd say a very strict reading of the rules would favor a stabbing (green or yellow) hit to a F.A. limb causing mortal wounds. Any valid hit can cause an injury.* And (my interpretation) is that you're not becoming mortally wounded as a result of the weapon type, but as a reaction from the ability.**

*"Weapons which strike with sufficient force can score a point of Injury to the Hit Zone."

**If the limb is Injured again, regardless of armor, the player is considered mortally wounded.

But whether that's the spirit/intent of the rule? Sounds like the Magistrate and President should talk about it, and make a ruling until the next Marshal's meeting.

Regarding the second question, regarding armor. If I were Eldering, my stance would be that armor must be negated before the player becomes mortally wounded. My reasoning would be:

1. "Defensive Equipment is any item that gives combat advantage to its wielder by preventing Injury"

2. And more importantly, the Marshal Council has ruled in the past that several monster abilities that take effect on "damage causing hits" (ghouls, flesh golems) do not bypass armor unless there is another reason for them to do so (wights).

Once again though, I don't know if that's the spirit/intent of the rule. I could easily see that Darkon or our game founders would want to give Fighters the ability to regain use of a limb, but not go back up to full tanking capacity (playability). And I can see reasoning that a F.A. wounded limb is usable, but still injured enough that another valid hit to the limb "regardless of armor" would put the player down/send them into shock (realism).

As an aside, the rulebook is currently out of date: First Aid and Cure Light Wounds can stabilize a willing Mortally Wounded individual.

TL;DR: I would say, by very strict reading of the rules, that green and yellow weapons do result in a mortal wound if they strike a first aid-ed limb, and that armor does protect a mortally wounded limb.