Probably not that big of a deal if they stop supporting IronRuby. What's the point anyhow? Ruby is most popular because of RoR and Microsoft already has an MVC framework that works just fine. There was some very limited effort to port ASP.NET MVC to IronRuby, but it looked dead in the water to me. Plus, I hear straight up Ruby has built-in bindings for Windows, so IronRuby isn't necessary for scripting either.
And that's where people miss the point. Is there any passion towards Microsoft's ASP.NET MVC thing? Because there a lot of passionate Rails enthusiasts around and it runs very well on top of the JVM.