Just out of curiosity, you said you were engaged in the Drassen Counterattack, does Skyrider dies in that attack or is there any automated battle in said attacks? Happens to me once, where i was auto the battle in B13, the airport since my merc was injured from previous attacks and sadly out of ammo so i though with 40 light blue militia would be able to fend off the attacks, since i had previously whittle down the attacking forces surrounding drassen.
Found out that after that im missing skyrider and my log did not register his death, after that heli is out but im managing with icecream truck and eventually hummer so no worries for me there.
Oh btw i played the 1.13 version though not the vanilla JA2.
I don't know if it was the official Drassen counterarrack or just a regular invasion, but when it happened my mercs weren't there because I was busy trying to retake a SAM site. I autoresolved it with militia, so you are probably right on the money when you say that Skyrider somehow died in that attack. My log did not register a death either so my best bet is that this is just some bug. Really annoying but not gamebreaking I guess.