@Rick Albert The insurance company Proper specializes in insurance for this situation. The tenant (me) can buy a policy which covers the landlord's building, enough to rebuild it from the ground up. Even in the event of intentional damage from the subletters (something typical renter's insurance does not cover).
Unfortunately such a policy is very expensive -- something like 8x the cost of typical homeowner's insurance. On a quote for a 4-bedroom house in Decatur, GA, the number was $4200 for a one-year policy.
I believe there is also a way for the landlord to buy insurance that has the same effect, but I'm not sure of the details.
As for if the law changes, there are several ways to handle that:
(a) Build in a lease-break clause. E.g., tenant (me) may give 60 days notice and pay a one-month's lease-breaking fee to terminate the lease.
(b) Give the tenant the right to vet and place a long-term tenant (background, credit check, income verification, rental history), with the landlord's approval, in order to take over the lease.
(c) Allow the tenant to end the lease in the event that it becomes illegal for him to short-term sublet (with or without some stated penalty).
My experience is very limited, but I've run into all three of these options (or some combination) in Atlanta. One landlord volunteered an additional clause saying that if occupancy was too low (<30% for three consecutive months), then I could end the lease with no penalty. However, he wanted 10% profit-share on top of the usual rent in order to cover his risks.
About the law changing: I suspect that in most cities where this happens, there are several months of notice, at least, between the passing of the new restriction on STR and the day that it comes into effect. So the tenant and the landlord both have warning, which helps keep things viable.
@John Underwood I'm not sure about the switch to a commercial policy, but you may be right. I've found it difficult to get details on the landlord's side of the insurance situation.
I will probably be PGing my first few arbitrage contracts. I believe it's typical for arbitragers to start that way and then switch to No PG after they have a proven track record and substantial cashflow.