Hi , say i have k8s cluster with longhorn and application pod writing data to PV's .. Then if i uninstall k8s and longhorn , will data be deleted from disk as well ? If i want data to be retained and restored after k8s re-install , is it possible with longhorn ?

what is your reclaim policy of PV(s)? https://kubernetes.io/docs/tasks/administer-cluster/change-pv-reclaim-policy/ And, look at backup solution like Velero or Kasten. So that in situation of cluster outage, you can restore from your backups

OR use longhorn’s backup function to S3.