There are loose parallels to the fates of the three guys who escaped from Alcatraz in 1962, and whose bodies were never found. http://www.npr.org/2012/06/12/154766199/50-years-later-myste... and also: http://www.bbc.com/news/science-environment-30349106
Survival theories end up getting very contrived in both cases. The rational side of me votes "Dead," but I can still be lured into reading an occasional speculative piece that tries to go somewhere with the last sliver of doubt.
In Cooper's case, the potential landing area was so vast & rugged that I'm guessing even the stubborn souls at the FBI couldn't pull off anything resembling an effective, quadrant-by-quadrant search for remains.
Would bones left out in the open still be identifiable? Or are they most likely dust by now?
How extensive really is surveillance of bill serial numbers? I mean, sure, he couldn't show up to close on a house with suitcases fully of those bills, but if it's not every routine deposit at every bank, seems possible that he could have spent it slowly.
Beyond the police angle, metrics on how quickly money is circulating is probably useful data for Fed economists.
It seems unlikely that in 1972, or even today, you could inspect anything but a minute portion of the cash in circulation.
He definitely could have spent it without it being detected, especially overseas.