Even throughout the rumor stage, there haven't been any whispers about changes being made to Sunset Blvd, so I would assume that the theater is safe. At some point, Beauty and the Beast is going to have to give way to something more current, but there hasn't been any mention of that. So for the time being, let's assume that it will continue to run, though personally, I would prefer to see the shows rotate. The Hunchback show was the best live performance that WDW ever had, and it is a shame that it cannot rotate in with Beauty.
As for Frozen, isn't the sing-along seasonal? Have seen nothing about keeping it or replacing it. But...the treatment that Frozen is getting seems pretty slap-dash and temporary until something more substantial and permanent can take its place. Will that be Epcot's makeover of Norway? Don't know. Personally, I would think that if DHS is going to get a major Pixar and Star Wars makeover, I don't see the fit for Frozen. So I would not be surprised to see the sing-along go away, or be moved elsewhere. Or remain seasonal.