Returning unused premium makes it a "mutual" insurance company, legally. This has specific legal and tax implications.
One of the big constraints of insurance companies is the differing laws in each state and province, so don't underestimate the corporate/legal/tax/accounting/operational/compliance reporting/etc costs in EACH jurisdiction.
As far as I understand, most US corporations legally reside in Delaware, and patent trolls like to file suit in East Texas, so the burden of this might be considerably less than for insurance sold to individuals.
One of the big constraints of insurance companies is the differing laws in each state and province, so don't underestimate the corporate/legal/tax/accounting/operational/compliance reporting/etc costs in EACH jurisdiction.