Hm, looks like you can get at least one different message if you haven't completed David's quest. In the mushroom cave:
You stare into the orb, turning over David's request in your mind.
In the depths, darkness swirls like ink in water, outlining a moving image. A young man rests in a chair surrounded by some sort of electronic equipment.
Although he's wearing some sort of visor, it looks strikingly like a younger version of David. A doctor enters the inky view to inject something into his arm.
Darkness fills the orb, except for a single mote of light where the young man was lying. Dark shapes prowl in the shadows like circling wolves, although you can't make them out clearly.
The mote expands, dissolving darkness into more light… constructs of light flitting around like butterflies.
It doesn't make a lot of sense at a glance, but perhaps David might have some input.
I'm guessing that this lets you complete his quest, but cannot actually test that, as I picked a survivor already.