they don't have brains so they don't think. no conscious decisions, but they do have an "instinct". that instinct makes them move away from a less than ideal environment. make sure your parameters are as close to perfect as possible and your lighting is strong. if the light is too strong, it will stay towards the bottom. if it's weak, it's gonna travel towards the light.
to answer your question- there isn't any way to know for sure if it will get sucked into a power head or not, and even if they do, it's not going to kill it. it will just be tangled up and look ugly for a couple days until it frees itself.