Unfortunately there's no way to save dr dalin during this mission, it's one of those fixed story moments that plays out the same every time. When you reach the experiment scene with the monolith artifact, things are gonna go south no matter what choices you've made before. The interesting part is, even if you've been working with strider or sided with the ward earlier, the outcome stays exactly the same - dr dalin either dies or vanishes during that experiment sequence.

You'll want to focus more on other decisions that actually matter, like your relationships with the different factions around the zone. Those choices definitely have consequences later on, but this particular moment with dr dalin, well it's meant to show you something important about sircaa and clear sky's activities. Just keep in mind that while you can't change his fate, how you handle the aftermath and who you trust afterward can make a big difference in your story.