I never read much SciFi but I have enjoyed scifi movies- not so much Star Wars stuff of shoot em ups. The topic has more recently become much more interesting to me.

My personal view is that your friend is boxing himself in, kinda like starting at the end and doing flashbacks to fill in the causes. I once thought the easiest way to write a mystery was to write up an interesting story, a murder or some such, and then mix up the chapters with the last chapter in front, etc.

As to your friend, I suggest, if he is set on that particular project, to have his space travelers arive at the planet, observe the strange behavior of the populace, learn that they are going to commit mass suicide, and then search out the reason for same while trying to disuade them. A valid reason could be an earth style cult conditioned to beleive that space travelers arrival would be the sign for their new life in "heaven" and our travelers unknowingly trigger the predictions by their arrival. Of course, as with all novels, this meager plot must be streched out adinfinitum.

Pass it along, you may lose a friend.

I enjoy any reading material, including subjets that could be classified as scifi if they have very imaginative creations. I have a book I started possibly 14 years ago close to being finished that remains undone because I did not feel my hero's creation and space experience was unique or imaginative enough. I go back to it every now and then but it sits waiting for the required spark to make it more worthwhile. There is no point writing about the obvious and or the commonplace. Cheers.