This is subtle, but I've thought about it and come up with the following, though I'm sure a more knowledgeable grammarian can put meat and perhaps clothes on these bones.
The two sentences mean the same except for the perspective of the speaker. To more clearly see the perspective of the speaker delete never from the sentences. Using the present continuous the action, perhaps influenced by the proximity of the speaker to the gates, is now; whereas the simple future would be used particularly if the speaker's proximity to the gates is actually distant and not within sight of the gates. Once you have got the idea of perspective, inserting never doesn't alter that.
By the way, I've not seen Frozen.