"purposely" fumbling forward.

[Cruser]

"He cathches the ball on the 6 yard line and as he is being tackled, around the 5 yard line, he "fumbles" the ball into the end zone. His teammate A2 falls on the ball in the end zone."

Wouldn't this be an incomplete illegal forward pass?
B should decline the penalty since the illegal forward pass was incomplete.....Game Over.

Going further, should you blow this play dead if it is clearly an "on-purpose" forward fumble that hits the ground, therefore making it an incomplete illegal forward pass? I'd like to see some opinions on this.