Has anyone here relight a submerged water heater after their basement flooded?

What price do you put on your life and that of your loved ones? You are dealing with natural gas, and it is very dangerous. The control valve can and will fail after it has been submerged. The sealed burn chamber is to prevent flammable fumes from entering the burn chamber. If you remove it, you will waive any warranty that was applicable to the heater. Only certified tech's or plumbers are allowed to remove this cover. Get a new heater, and look into a permanent sump pump. This will eliminate the problem in the future. Good luck!