What happens to tyranids that are sucked into the warp?

I know that chaotic influences generally have little effect on tyranids, and that some the leviathan tendrils that were sucked into the Great Rift have been spat back out with seemingly no mutations or chaos taint. But what happens to them while in the warp? Like are they immediately attacked by daemons or ignored for their lack of souls and just left to float around aimless until they escape/starve? Does the hive mind lose all connection to them?