Launch day is a checklist, not a ceremony: old addresses redirected so your search rankings survive, email untouched, forms tested one more time, backups running. Then we stay. Content and media updates within 24 hours. A report every month that says what happened in plain words. And regularly, back to the drawing to decide what to build next.
You hold at the end: a live site, a redirect map, a monthly report, and someone to call.