Comes down to "what's it worth to you?"
While good oars are expensive, drift boats are expensive (to an extent) as well. Busting an oar in a tricky rapid is dangerous.
Another vote for "spare." Although bringing standard 9 footers as spares is kind of lame, it goes back to "expense." The collapsible ones are the bomb, but they aren't super-cheap, especially for something that you'll likely never use.
So again, it's "what's it worth?" But using a shaky oar is something of a safety issue.
Just my overpriced $0.02.