People are saying she'll be safed on account of footage/screenshots that shows 1. Sora holding the Master's Defender 2. Sora reaching for Aqua's hand through the water 3. The fact that the Dark Margin and Destiny Island can connect to each other in some ways.
But despite this "evidence" that they're using, they seem to have forgot that Sora did not go to Destiny Islands at the end of 3D (at least it's not confirmed). He went to the Realm of Sleep, to see his Dream Eaters. So for what we know, that could be his "secret". A bit underwhelming, but that's what we know. There was no reason nor indication that Sora was heading towards Destiny Islands, so he's probably heading back to Yen Sid's Tower after he's done thanking his Dream Eaters.
Besides, it would be better for KH3 if it had a mission where Sora (or Riku) saved Aqua. Save the heavy story related content for that game is what I say.
The 13th Kenpachi reacted to a post in a topic:
Nomura stated that Aqua will not be saved in 0.2 BBS but in KH3