So, I think I fount out what is causes saens to die, it isn't OOM as I thought, but it seems the process table is full. I installed watchdog+softdog and the machine sucessfully crashed and rebooted with log messages from watchdog indicating that it was unable to fork due to EAGAIN which kernel source seems to indicate no more task entries.
The question is why - which is why I wrote this single process pid logger thingy jiggy to watch out. Some buggy daemon is creating excessive processes, bets are its proftpd. I had forgotten that I ulimited the hell out of proftpd ever so long ago, so OOM it aint.
Why do we use this? Why do all FTPd suck? All I want is a bullet proof, fast anon-only ftpd that meets the DFSG. Sigh.
Of course with my luck it will be apache or some weird ass kernel bug. At least it reboots itself now.