If your computer doesn't detect that Kindle as a removable drive when you connect it via USB cable then you are definitely out of luck. Since PW5 doesn't even have serial port connection pads on its motherboard there is no known method of de-bricking a Kindle PW5.
That was the case with my first PW5 when it bootlooped: both Windows and Linux PCs didn't detect the USB device even for a second
And because of couple of reports here on Mobileread of PW5 getting stuck while running KOReader in standby / sleep mode and bootlooping after forced reboot on my second PW5 I'm being extra paranoid and I always exit out of KOReader when I've finished reading.