Is it possible to restore a accidentially deleted TFS 2015.3 Release Definition?
The definition has been deleted by mistake but I've read somewhere that it's possible for build definitions by directly connecting to the TFS database and updating the IsDeleted flag of a build definition table row.
Are there any options for a release definition?
The modifications in operational databases are not recommended and are not supported by Microsoft.
But you can update on your own risk the [Release].[tbl_ReleaseDefinition] table.