Are the Zehoberei Extinct?

In the comics, the Zen-Whoberi were completely annihilated in a possible future by the Universal Church of Truth when the race declined the offer of joining the cosmic cult. Gamora was saved by Thanos during the massacre and brought back in the past, when her race was still alive.

Why did Thanos destroy Gamora's planet?

The Sacrifice of Gamora was the ultimate step that was required in order for Thanos to obtain the Soul Stone. When the Red Skull informed Thanos that he must sacrifice something that he loved to obtain the Soul Stone, he threw his adopted daughter off the cliff with great sadness.

Is Gamora last of her kind?

According to Guardians of the Galaxy, Gamora is the last of her race, the Zehoberi people. Her entire world was slaughtered by Thanos, leaving her the only survivor.