@silver18: Upstart runs its script portions more or less like a shell in 'honor return codes' (-e) mode. Meaning if *any* part of the script returns a non-zero return code, the full script/job will fail. Which might possibly halts the boot process, I'm not familiar enough with upstart and the job tree on the Kindle to be definitive on that, and I don't really want to be, so I just handle it with a touch of paranoia
In the OP's examples, that means that if the file it tries to run doesn't exist, it'll fail to start the job, possibly not very gracefully, possibly halting the boot process.
So, simple workaround, check that the file exists before running it, (and eventually return 0 at the end for extra paranoia ^^):
exec /bin/bash /var/local/dev/somescript.sh
[ -f /var/local/dev/somescript.sh ] && exec /bin/bash /var/local/dev/somescript.sh
Also, on a sidenote, I have no idea if relying on 'exec' in the script potion of an upstart job is safe at all. I'd just live with the fork, and just run it relying on the shebang.