Kav Landseeker’s last ability creates a delayed triggered ability that triggers at the beginning of the end step on your next turn. When that ability resolves, if you still control the Lander token created by Kav Landseeker’s last ability, you’ll sacrifice that token. Sacrificing the Lander token this way won’t allow you to search your library for a basic land.

If a replacement effect (such as that of Exalted Sunborn’s second ability) causes additional tokens to be created during the resolution of Kav Landseeker’s last ability, you’ll sacrifice those tokens at the beginning of the end step on your next turn as well.