If your goal is to update your form to a new version that you had previously downloaded to disk or to revert to an older version previously downloaded to disk, do not first delete the form since, as stated, this removes all associated saved/submitted/pending form instances. Instead leave the original as it is and upload the version from disk by clicking theupload icon. A dialog will display that lets you browse to the form on disk and gives you the option of replacing the current with this new version. Checking the option to ignore XML schemas in the form being uploaded if those schemas already exist in the application, results in the existing schemas being used.
When uploading a form with the same ID as an existing form, without checking Replace, a copy will be created and the designer will see an error message: "The flow that was uploaded matches the id of one that already existed so a copy was made. If you intended to replace the existing flow, delete the flow you just uploaded and upload it again but check off the ‘Replace’ option."
When uploading a form with Replace checked that is currently being edited by another user, the designer will see this error message: "This flow is currently being edited by <user@tenant>. Please try again later."
Designer users can grant other users the ability to edit a form and access related submissions. The Access Control and Shared Items topic explains the details. This permission gives Users with this permission also can run the process to Refresh Searchable Fields.