An edit session can’t be posted to the VEP dataset until all edits are approved within the session. When the edit session is rejected by the Admin, it will become available in the review widget for the Editor to review and revise before resubmission. An edit session will only be gone for good if it’s deleted by the Editor in the Edit tool or an Admin in the Manage Version page, so there is no risk of losing the session by rejecting it.