After some digging, I found another site that reported in December that Sonia actually sold her brand back in September 2015 to Target, and has only been hanging on as creative director. And according to Sonia's Instagram account, this past Spring was her last collection for Target before stepping down permanently.
So what does this mean for the brand's future? MusingsOfAMuse predicts that Target will keep Sonia's brushes and makeup bags, but may phase out the makeup to make room for newer brands. But I don't think this is happening in the immediate future, as a quick check of Target.com shows over 200 Sonia Kashuk products in stock, and only 2 of them are on clearance.