Using regular water heater for hydronic radiators
It's actually not uncommon to use a water heater for heating a well-insulated building (though an electric water heater is very UN-common, due to operating cost.) But....

This is not commonly done with radiators, which are typically designed to operate on 180F water. It is much more common with radiant floor heating, which can function quite well down at 100F water temperature in many cases.

The building must be well-insulated - the typical reason for using a hot water heater is the inability to get a "boiler" that's SMALL enough for the load of a well-insulated building. As designed, my shop will take about 30K BTUs/Hr to heat to 68F on a -20F "design day." (the minimum temperature used for the sizing the heating system.) A 100K BTU/Hr boiler would be massively oversized.

You need an expansion tank for a closed system, and you may need to use stainless steel pumps (rather than cast iron) if any part of the system allows oxygen to get in (non-oxygen barrier tubing, or an open system where the SAME water heater heats the floor AND the domestic hot water - in which case the floor tubing needs to be potable-water rated - not actually difficult to find in PEX tubing.)

Finally, if there is gas in your area now, it's stunningly unlikely to "become unavailable" in a future where you still have electricity. And if you are "heating with electricity" you really should be using a heat pump (in cold climates, a cold-climate air-to-air heat pump or a water-source/geothermal heat pump) since you get about 3 times the heat (depending on conditions and specific unit) for a given amount of electricity purchased. Heat pump water-heaters won't work without some other source of heat, as they are designed to operate from air that's 50F or more, typically.