Face it, most of the data I store are simply storage, and extremely seldom used (even OS files). So, even the cache on the SSHD is enough to hold almost all the files actually used. For example, a large compile that takes over a minute on HD is done in seconds on my SSHD.
As for how long the longest lasting drive held out, I find that pretty uninteresting. It's the one that failed first that I find interesting.
As for flash memory dying, I've had several memory cards and USB sticks die on me, especially USB sticks.