There are entire towns at the Jersey shore built on leased land. Ocean Grove comes to mind. The building owner owns the building and has a 99 year land lease, usually.
And yes those mortgages have flood insurance provided by the building owner.
What happens to the building after the end of the land lease depends upon the terms of the lease and the wishes of the parties. Renew lease, move building, revert to land owner, etc.
These kinds of ownership questions need discussion with legal counsel to make sure you are documenting your loans correctly to protect the bank, let alone flood insurance.
Kathleen Blanchard CRCM "Kaybee"
CRA/HMDA Maps,Analysis,Consulting,Geocoding,Compliance Services