There is greater chance of flooding from leaking filters or over filling from WC than from tank failure. I am not aware that glass tank in continuous use can fail spontaneously from old age. There is life span of O rings in canister filters, but not the silicone seal in glass tank in continuous use. Flooding accident can occur because the hose in your sump system or canister comes off, and even a tiny air pump hose coming off can drain the tank if undiscovered over a weekend. Tanks usually fail from unstable placement, impact from moving, or drying of silicone seal in garage storage. As far as insurance coverage, I am not aware of exclusion clause of fish tanks in home policy. If you are paranoid about flooding, place all your fish tanks in the garage or basement where flooding can't do much damage. To me, a show tank is a living art that belongs to the living area where everyone can appreciate, and it makes no sense to hide it in the dirty basement no visitors can appreciate.