I'm still coding some bonuses, and this might be one if we can think of a way to code it "simple" but also "useable"..
Caveats
It's important(ish) that when a URL is in the search engines...that URL stays as it is.
With that in mind
1. new admin page where you can make "redirects", eg;
Blue Widget -> Purple Wodget
Red Doofer -> Pink Doofus
2. content module for product_info, this grabs the redirect and
outputs a message "discontinued but we recommend..."
So, if they end up on the "Blue Widget" page, they see;
<div class="alert alert-danger">
<p class="lead">This product is discontinued...</p>
<p>We recommend our <a href="abc.com/product_info.php?products_id=123">Purple Wodget</a> instead...</p>
</div>
That is workable and simple...
And, no core code changes...