I agree. I don't think that there's any other option. There are rules in this community as to who is going to get released and why. Those rules don't seem to be negotiable.
So I don't think that there's any other possibility for what would have happened to Gabe. He was going to get killed and there was nothing that could have changed that other than Jonas taking him and running.
Gabriel was scheduled to be released. Originally, Jonas had planned to escape more carefully and with more preparation. However in chapter 21, Jonas learns that Gabriel will be released.
All newchildren need to meet certain growth markers to be accepted into the community. Babies are carefully monitored to make sure they are growing at the right rate, sleeping through the night without crying and developing “normally” as the community thinks they should.
Unfortunately, Gabe did not meet enough of these markers. Jonas’s father begins taking him home at night for extra nurturing, and Jonas starts to give him memories to soothe him. When his father decides to leave Gabriel at the nurturing center at night to see if he has matured, he cries all night.
“So,” father went on, “We obviously had to make the decision. Even I voted for Gabriel’s release when we had the meeting this afternoon.”
To avoid Gabriel’s release, Jonas takes him and flees, leaving the community before he had planned to.
Elders had a plan to "release" him because of having some problems at night. And if he stayed in the community, father would release him exactly.