First of all, we don't know the nature of the failure. Didn't the report say he saw the rudder floating behind the boat?
I don't know how the ruder was installed, but on most boats I've seen, if the rudder fell out of the boat, stock and all, the big hole it left behind would sink the boat pretty quick. How many boats have even a partial bulkhead forward of the rudder to prevent flooding?
Neither do we know what kind of rudder was fabricated. I saw in the report that they left from Mindelo and that BoatCV did the work. Mindelo is the biggest town and port in the Cape Verdes. It has a couple of shipyards (it was a coaling station operated by the Brits for steamships for about a hundred years). There is no shortage of trades, but whether the skills are up to a job like this -- who knows. (Most of my info is from Don Street -- I edited his Street's Guide to the Cape Verde Islands. I was in Mindelo for one night in 1971.)
If it were me, in a bit of a hurry to set off for the Caribbean, I wouldn't bother with an authentic replacement but I would have a rudder welded up of steel and filled with foam to get me out of there.
I suspect the failure was the stock. Maybe they used the wrong (only available?) schedule pipe. I could very likely be wrong.