@Ahmed, Adeel (FBAU) Thanks for reaching out, once you delete the APIM instance all the backend configurations will be deleted permanently. As an alternative you can use backup and restore option you can create a new APIM service, backup the old one and restore it in newly created service.
for more information please refer: https://learn.microsoft.com/en-us/azure/api-management/api-management-howto-disaster-recovery-backup-restore#-back-up-an-api-management-service
Backup and restore has few constraints as well please refer: https://learn.microsoft.com/en-us/azure/api-management/api-management-howto-disaster-recovery-backup-restore#constraints-when-making-backup-or-restore-request