When an amount wired out incorrectly is noted, what is the recourse for getting it returned?

Ask the beneficiary's bank very nicely, and include plenty of language to indemnify them in case the beneficiary gets mad at having the windfall taken away. Hopefully it won't cost you too much if the beneficiary says "no" to the request. Some lessons are more costly than others.

haven't we beaten this dead horse enough?

This "windfall" is taxable, I presume. I have asked several people if the funds have been spent, how do you go about getting them back, realistically. Garnishment of wages?