Things to consider about the decision to take the wounded bird home-
The news media seem to know right away that a collision occured, where it happened, what make, model year of aircraft and how many people on board. How did they know all this? If we are to believe the flight tracks attached here from another forum, both planes were squawking 1200, so likely
not talking to ATC. The news media also reports that boat traffic responded right away.
Given the above, the most likely scenario is, Dreadnought's pilot informed ATC on frequency of the accident, watched his friend go in the water, saw the boat traffic respond as well as other planes on frequency and decided to look after his own problem. Really not a "hit and run".
On his decision to continue on to his intended destination, we have already discussed the compelling reasons not to land at the nearest airport, so the question remains as to how safe was that plane? If we are to believe the unsubstantiated rumor that the damage was to the vertical stabilizer, then from the photo below, you can see that he and his wife would have a pretty good view of that damage.
Now consider that this PIC unlike most, has intimate knowledge and understanding of just exactly how this plane is built down to the rivet. He also has likely thousands of hours in this type by now and can detect what is and isn't quite right. In addition, being a Reno air race pilot for many years, he may have experience with piloting damaged and malfunctioning planes. Also consider that this airplane was originally built for combat and high speeds. It is considerably more robust than the average Cessna.
Seriously, I think putting it down at Napa, or Concord, or Oakland would just have been a huge waste of time, expense and bother for very likely nothing. I have to give the PIC in this case the benefit of the doubt without any real facts known. I don't think he was trying to hide something, or run away from the scene of an accident and I have to defer to his expert opinion on how safe the airplane actually was. At this point, I believe what he did was reasonable.