Some observations.
1. This FIA satellite was in low enough orbit that atmospheric drag will eventually bring down all the pieces. Anything having a non-round profile will have high coefficients of drag. So the pieces will come down.
First, you may be completely correct, hopefully you are -- we'll know in a few days what, if anything, is left. Second, I agree, the Navy did a good job. As much as I hate to admit it, the Navy does a better job at a lot of these things than the Air Force. But, they don't have as much time to play golf.
Now, as far as the pieces coming down, yes they will eventually come down but here is the potential problem, based on having been a spacetracker for several years when on active duty. It's about delta-v. When the collission happened it would most likely have been head-on. Most pieces coming off the satellite would receive a negative delta-v, in the direction opposite the collission vector, as what happens when two billiard balls strike. That's good, because the pieces are slowed down and they reenter even faster.
Some pieces will receive delta-v at other angles, though, and the problem would be with pieces that received positive delta-v. That can happen because you are striking a big object with a small object. At closing speed of 10 or more km/sec, parts of the big satellite would be ahead of the collision point when propelled forward by parts of the collision, whether physical particles or outgas explosions from the vaporized hydrazine.
Parts that get positive delta-v act as if they have been injected into a minimum energy (Hohmann) elliptical transfer orbit. Their previous position becomes a new perigee, and they go into an elliptical orbit with apogee at a higher altitude depending on the amount of delta v they received. I did some back of the envelope calculations, and figured a delta v of 3 km/sec, about 30% of the collision velocities, would be enough to transfer a piece into a 2000km apogee elliptical orbit. That piece would still come down to the lower orbit at perigee, where it would encounter the higher drags that you mentioned but, based on orbital models, they would have a lifetime of a year or more (orbital debris models are highly inaccurate, especially for elliptical orbits). And what makes it more of a problem is that an elliptical orbit of that nature intersects the LEO orbits of many other satellites, including the space station. Still, there's a lot of space out there, so the chances of a collision are small but nonzero.
Bottom line, I'm not disagreeing with what you said, in fact, you are probably correct. Just pointing out the uncertainties, and the fact that orbital debris is very hard to predict or track. The smaller the piece, the more unstable the orbit, and oftentimes we don't even know a piece of debris is there.
Now, having had to refresh some brain cells from long ago, I do not guarantee the above is completely correct. In fact, hope I got it wrong so I don't get recalled.
P.S. You may have a point with the cryptos, hadn't thought about that.
Hopefully the first one will score a direct hit, and hopefully they have an HD camera strapped to a high altitude plane of some sort taking good footage we can all watch on youtube!
