Had this clarification today from Microsoft on the status of Sandbox Solutions:

“The only thing that is deprecated is sandboxed code. If you created a sandboxed solution in VisualStudio and set the “Include Assembly In Package” property to false, this is a declarative-only solution and that is not deprecated”

So basically provided there is no code in your sandbox solution you are good to go and that is not being removed from SharePoint 2013.

Hope that helps clear-up the rather confused messaging from MS about this!

Cheers

Dave Mc