As Tanjiro bides farewell to Sakonji, he asks him to greet Sabito and Makomo for him, leaving Sakonji confused. Hinting at the fact that the two were actually ghosts, Sakonji wonders where Tanjiro got those names from.

Is Sabito still alive?

In an attempt to kill it, Sabito's blade breaks on the demon's thick neck, and he dies by the Demon's hands. Sabito was the only one who didn't make it pass his year's final selection.

Was Sabito stronger than Giyuu?

Sabito was indeed stronger than Giyu. He spent the entire final selection saving his fellow demon slayers. Giyu admitted that if Sabito survived the exam, he'd likely be the Water Pillar instead. In chapter #131, Tanjiro became tasked with convincing Giyu to participate in the Pillar Training sessions.