It is possible that doors and windows and wardrobes were broken. Can steel or titanium sheet survive this? It might probably has been swept away from the house into the ocean.
Physically (chemically) a steel (if stainless) or titanium sheet will withstand flooding (water), and the person who finds your seed phrase on it will thank you for such forethought.
A piece of steel metal will rust in water and staying it in water for a long time will make the seed phrase unreadable.
In the event of a flood, the threat comes not from the impact of water, but from its consequences: when the water recedes, then with the ebb of the tide, unfixed objects can float away, even metallic ones, especially small ones like your sheet.
You can avoid this in a simple way:
- store the sheet on the upper floors or in the attic, where water ingress is unlikely;
or store it in the basement, from where the water will not go up when it decreases, but will remain below ground level, which means that the sheet will not float away being carried away by the current.
- be sure to fix the sheet on (or inside) stable structural elements of the house, such as walls, beams, foundations and the like.