I’m sure it would have been, were they focused on Syndrome at all at the time in happened! But I honestly think 100% of their attention was on their infant who was free-falling hundreds of feet. (Even had they known about Jack-jack’s powers, that’s still a terrifying thing to see!) Helen wasn’t even facing the jet when it exploded, she was preoccupied with trying to console Jack-Jack and to telling him to look at Mommy, not the huge explosion. 😂
I do think had they been looking, it would have been an upsetting sight, especially for Bob. The way I headcanon it, he actually saw Gail get sucked into the turbine, although it was from pretty far away. As much as I’m sure they loathed Syndrome, I don’t think Helen or Bob wanted him to die. Punished, surely, but not like that.