Before sunsetting a theme create a Canvas skin
Woothemes has alienated many customers using industry-specific themes that are "no longer popular".
I recommend that you first create a new Canvas "skin" that is similar to the old theme before sunsetting the old theme. This way your customers at least have a option vs. you just shutting down support for a theme.
Joe Jenkins commented
I've always thought that it would be good to have Canvas themes. There are many tutorials and code snippets for canvas around the web, and this would be a great opportunity.
I'd second the Scrollider as Canvas child theme. I love Scrollider, but I can't (easily) tweak it like I can Canvas. Well, you can't (easily) tweak anything as easily as Canvas.
Brett Blevins commented
That's a really great idea! That "skin" would technically be a Canvas child theme. I'm thinking about doing this myself because one of those industry-specific themes was cancelled. I always make child themes, anyway.
I like this idea too. I'd give my left nut for the blog of scrollider in Canvas. I find Canvas' blog kinda stale. :(