Would you warn them that V'ger was going to take Ilia?
(I got a copy of the "special longer version" in the mail today, and have it running as I type. And yeah, I'm especially enjoying it. Been a long time.)
No, I wouldn't warn them. It is my opinion that sheer luck is what resulted in the prevention of Earth's destruction. Any deviation from the events that took place in TMP might result in destruction. So, no.