gform_after_delete_form

add_action( 'gform_after_delete_form', 'do_cleanup' );

function do_cleanup( $form_id ) {
    // Perform your cleanup actions here
    // $form_id is the ID of the form that has been deleted
}

add_action( 'gform_after_delete_form', 'log_form_deleted' );

function log_form_deleted( $form_id ) {
    $log_file = ABSPATH . '/gf_deleted_forms.log';
    $f = fopen( $log_file, 'a' );
    $user = wp_get_current_user();
    fwrite( $f, date( 'c' ) . " - Form deleted by {$user->user_login}. Form ID: {$form_id}.\n" );
    fclose( $f );
}