will these activities still be there this summer?
Anna and Elsa are reportedly a permanent fixture at the Animation Building in Hollywood Land. I think they are there to stay.
As for Freeze the Night -- there is a rumor that Mad T Party could, perhaps, return in May. If Freeze the Night is popular enough, I think we've seen the last of Mad T Party, but we'll see.
Both Olaf's Snow Fest and the sing-along at the Muppets Theater (a.k.a. the Crown Jewel, or whatever it is called now) are supposed to just be in place until May. However, I would not be shocked if we see them stick around beyond May -- or possibly leave and come back soon after, "by popular demand."
The DIS Unplugged team recently commented in their podcast about the fact that none of these events feel very "temporary" -- most of them have a permanent feel to them.
The Arendelle addition to the Storybook Land Canal Boats is permanent.
The current show at the Royal Theatre in FL is all
Frozen right now, but supposedly the regular shows will return after a while.
Olaf's Frozen Ice Rink and the Winter Village in DTD are there through February 22nd.