I want to live in a world where tarsnap is sold for picodollars.
I know I am and that this 14 days clause is the only reason why I am not using tarsnap.
What if auto-renew were added, but you're robbed and knocked into a coma for 2 months. In the meanwhile, the credit card company notices the suspicious transactions, can't get a hold of you, and cancels the card. Auto-renew occurs 3 days later, but the card number on file doesn't work. Colin Percival calls your phone number, and gets no answer for a month. Then what?
If you're truly paranoid, you might have to consider that possibility as well.
With every scenario and solution you can come up with which require intervention, I can double down on and think of a worse-case scenario where your solution won't work and you'll lose your data. A possible non-intervention solution could work, which is to front-load the account to the limits of your paranoia.
1) Paranoid that you will lose your data.
2) Paranoid that your data will fall into the wrong hands.
It seems to me that Tarsnap values preventing #2 over preventing #1.
To follow on your example, what if the authorities who arrested you want to get their mitts on the data in your tarsnap account? Won't you be happy that your data is irrevocably deleted?