Nothing.
Family Sharing is not device dependent. If one device is lost, stolen or broken and cannot be used for any reason, the Family Organizer can log in to a new device and continue managing Family Sharing from there.
They can also continue to access and manage Family sharing from any other Apple device they may already have that is logged in to the Apple ID that was used to set up Family Sharing.
Family Sharing continues to exist and all subscriptions continue to be paid for and shared as long as the Family organizer does not cancel them or disbands the family group.