If the configure sink is not reachable, will the CDC events (changefeed) lost?
They are not lost, but you could restart the changefeed with a cursor with the time in which the previous changefeed failed.
They can go back as far back as the TTL on the table.
I hope this helps.
When the leader for a range becomes unreachable, will the Changefeed be served from the new leader? Will this happen without interruption? Will older changes (up to TTL) be available on the new leader? TIA.
As long as the raft group can maintain quorum then it will be served from the new leader. There should not be any interruption. The new leader would have previously been a follower and is updated with all changes, so they should maintain.
Please read our known limitations.