OK Hawk, I'll give it a try. First, If the receiving team first touches a scrimmage kick beyond the expanded neutral zone, the ball will belong to whichever team has possession at the end of the down and that team will be awarded a new series, i.e., first and ten. Because the ball bounded back behind the neutral zone, the kicking team can fall on it and it will be their ball with a new series at that spot; they can advance it and it will be their ball with a new series wherever the run ends; they can kick it again and, if the receiving team doesn't muff it again, it will be the receiving team's ball; or they can throw a forward pass. Because the pass is thrown from behind the neutral zone and it is the only forward pass during the play, it is a legal forward pass. So far, everything that was done during the play is legal. Now to determine who gets the ball and where.
According to the rules, the team in possession at the end of the down gets the ball. In this case, the kicking team was in team possession at the end of the down. Therefore, I would say that the kicking team gets possession. The where is an interesting question. Certainly, Red will not get the ball where it stops rolling. The other choices are at the spot of the pass and the previous spot. I can't think of a rule that would spot the ball from the spot of the pass. I would guess that it would be from the previous spot -- the 50 yard line.
All that having been said, I would spot the ball at the 50 and and award a first down to Red. I could very well be wrong. What bothers me is that this is a play that I can see happening and I am not sure of the ruling. In high school football we often see punts that are shanked for 10 to 15 yards that could easily be muffed back behind the neutral zone.
Something that is also likely to happen in this situation is Red having ineligible players downfield at the time of the pass. That would make it even more interesting.