A very simple way of doing it would be with a shell script in an infinite loop.
An example would be if your daemon was called foo, I'd write a script called run-foo.sh.
the contents would hold:
while true; do foo "$@"; done
so evertime the "foo" process dies, "run-foo.sh" begins to execute again and then starts foo back up.
There are probably bunches of other ways to do it too.