jdMorgan - 10:31 pm on Mar 17, 2011 (gmt 0)
Remove the Disallow from robots.txt. If you Disallow a URL in robots.txt, then you cannot expect to reliably redirect that URL because a robots.txt-compliant client will never request that URL.
Consider modifying your script to look up the "affiliate links" in a database and determine if they are currently valid. If not, redirect to remove the affiliate ID (if that's what you're getting at here).
I'd certainly consider redirection over a 410 or 404 -- You don't want to be throwing away the credit for the inbound links, do you? (I'm asking)