https://api.drupal.org/api/drupal/core%21modules%21migrate%21src%21Event%21MigrateEvents.php/constant/MigrateEvents%3A%3APOST_ROW_DELETE/8.9.x
MigrateEvents::POST_ROW_DELETE | Drupal API
postrowdeletedrupalapi
https://api.drupal.org/api/drupal/core%21modules%21migrate%21src%21Event%21MigrateEvents.php/constant/MigrateEvents%3A%3AMAP_DELETE/10
MigrateEvents::MAP_DELETE | Drupal API
mapdeletedrupalapi