If you would like direct calls to route to 1000 instead of 1001, you can set a fordward unconditional to 1000, and log them out of any existing hunt groups. That is easiest, as once a replacement is found, you can undo the fordwarding instead of checking the ICR and log them back into the group (you might forget to check if changed at the ICR, I know I do). It would still be advisable to have a leave action in the voicemail box to 1000, incase someone direct transfers to their voicemail box via #1001, and then removing the action once they are replaced.