Interesting. I've yet to get a mission to drop off supplies or personnel, but I would certainly complete those with or without torps. I didn't know if there was some sort of penalty for not completing a "proceed to area XX and patrol within 108 miles of that point for 4 days" mission. It seems reasonable to not get punished for not completing a mission like that when the reason is that you sank 30K tons or so of enemy shipping and were out of torps.... but until your response, that was just an assumption on my part. Thanks for the info!
Edited to add: I wonder what would happen if you had a mission to drop off supplies/personnel and, along the way, you had an encounter that damaged your boat to the point that it was unwise/unsafe to do anything other than RTB? (There goes that contingency planning mentality of mine again...)