Are the spirits of old cycle Avatars dead?

I know Korra is the last avatar of the old cycle and the first avatar of the new. But is it just the connection that’s lost and they are still there or has something happened to the spirits of the old cycle who carry the knowledge and memories?
If Korra started a new cycle does that mean we can never see Aang’s spirit again even if any new story comes up except in flashbacks? Or any of the other avatars of old cycle. I know the connection between Korra and other avatars was cut but is it just that since the visual in the show of them getting erased one by one seems like they are actually dying.

If so, does Katara know about it?

Also does that mean all the knowledge of the past is lost to next cycle Avatars?

I am a little late to the Avatar party but I recently watched both series and love the last Airbender series so much. The solace that the avatar is never really gone due to incarnation is lost if the old cycle died which is just sad.