my recipient has lost his funds.
Yes this is what happens in a double spend scenario
What if I've died, moved on, lost my private key, etc.. I can't reissue the transaction.
Then you are a small edge case, especially for plausible fork lengths, and even more especially for plausible fork lengths given regular checkpoints (as in Bitcoin and every other reasonable coin). Given the possibility of forks (even normal ones transient ones) you always need to be prepared to reissue your transaction for some reasonable period of time.
The far more likely cases are that: 1) nothing happens, or 2) you simply see the coins back in your wallet and resend them.
And please don't equate with waiting for 6 confirmations
I didn't. I said sufficient. That is a judgement call for the recipient to make. 6 is just a default number from Bitcoin but it really means nothing other than the output of a particular probabilistic model from Satoshi's paper, as you correctly explained. Recipients have to make their own judgements when dealing with blockchain technologies. Transactions are never really "final" they are just "final enough." Normal forks and accidental forks (due to software bugs) and deliberately-created forks and double spend attacks are all possibilities to consider, and all have happened before.