what happens to the family's subscriptions if an organizer left the family?

If an Organizer leaves the family the entire family group is dissolved. You then need to take out an individual subscription or have somebody create a new family, invite the old memebers, then somebody take out a family level subscription that can be shared. To learn how to set up Family Sharing, read this support article --> Set up Family Sharing - Apple Support

Note that if the family is disbanded you may lost access to content as well as things such as Apple Music playlists, etc. The family members need to take out individual subscriptions before the family is disbanded to ensure continuous coverage.