Mirmi: No, the Gur don't kill Astarion. If you give him to Gandrel, then Cazador will attack and kill the Gur and Astarion will get zombified during the ritual. Happened to a friend of mine,who wanted to find out,what happens, if you give Astarion to Gandrel.
When you meet them at their camp, the Gur explicitly say they were targeting Astarion so they could interrogate him and then kill him. How can the ritual zombify Astarion when it doesn't do that to anyone else? A video for reference where you can see that Astarion is already a zombie when the stage for the ritual had been prepared:
One comment mentions that: "There were some notes in the kennels saying that Cazador got pissed because he couldn’t control Astarion, so he flayed Astarion alive over and over again until Astarion couldn’t be put together in human form anymore." On one hand it makes sense given his sadistic nature, but on the other it's strange because the game shows Cazador can place Astarion in the ritual circle with ease. Also, he'd want to hear his screams during the ceremony, for sure. Now I wonder if it's the same when Astarion gets given to Gandrel and when he's not been recruited. Maybe Cazador found his corpse and reanimated him after the Gur did what they'd set out to do. Astarion is also a zombie if you staked him during the bite night.
Every time someone says ascension is Astarion's bad ending, they should be redirected to this video. It's beyond horrific. The only thing that makes it worse is Cazador actually ascending in this outcome so Astarion's soul gets sacrificed.