This doesn't hold for any other ability, though. Every ability activates and is resolved immediately, whether it says "immediately" or not.I would agree with this, but what makes me disagree is the lack of the word "immediately" on IG-88A. If it said "immediately after you perform an attack, if that attack destroyed the defender, then you may recover 1 shield", then I agree with you 100% that IG-88A's ability would not trigger. The timing condition would have passed.
R2-D2 Astromech: "After executing a green maneuver, you may recover 1 shield (up to your shield value)."
FAQ on R2-D2 Astromech and overlaps: A ship equipped with R2-D2 rolls for damage before recovering a shield. However, it recovers a shield before rolling for APL or asteroid damage. (APL triggers on "after [execution of the maneuver]", as well.) The "when a ship executes a maneuver" wording of Proximity Mines is what allows it to insert before the "after" wording of R2-D2, and you resolve the R2-D2 step after the Proximity Mine so rudely interrupted it.
In the core rules, the wording is actually just as clear. (I'm le shocked) It says, "Although ships perform their attacks one at a time, ships with a pilot skill value equal to the active ship's pilot skill value have the opportunity to attack before being destroyed."
The "before" word used here is what's important, imo.
So therefore, the simultaneous attack happens in between the damage assignment and the being destroyed events. Which makes sense. The simultaneous attack interrupts the resolution of IG-88A, but after the simultaneous attack is over (barring destruction of IG-88A), the regen of a shield should still happen.
That said, I'm not so sure about Fel's Wrath anymore.