In my experience only thing that causes N9 to "die" is the twl5031 (drivers are called twl4030..., and it's not really twl5031 but seems to be some custom made part with ACI/ECI) It does so when twl4030-wdt watchdog doesn't get kicked for 30s (see here: http://talk.maemo.org/showpost.php?p=1485818&postcount=20). You can't use flasher to disable that, because ubiboot starts kicking both watchdogs (essentially starting them if flasher had set them not to be started automatically) - so something has to kick them until shutdown.

If your are running "the stock kernel" (2.6 I presume) then the kernel is not to blame here - as we know that kernel is working OK. I would suggest you try the mentioned watchdog "thing" which may be enough to get some logs saved.

If you're interested I can post details on how to make serial cable without opening/damaging the device (that small cardboard piece with two wires sticking out in pictures is just inserted instead of SIM tray). - that might save you a lot of trouble.

Here is Nemo booting 4.3.0-rc5 captured with it: http://pastebin.com/raw.php?i=mZkmscN9 - as you see it's quite "informative"