happens all the time, hiring managers get used to it, about 30% of people never accept, usually because they have more
than one offer and/or a counter from their current company.
I had a guy give notice, we offered him a completely new professional track, and he's been stellar, he stayed for less money, with more future growth.
I've also had people who even showed up, after accepting and waiting 45 days for them, and then had the gall after 5 days to say that there really wasn't enough work for them. We decided to promote from within, and that person has two assistants to keep it all covered (facilities management is no joke for a facility this big)