Possible damage to water heater if bypassed while on?

Most likely the electric element is shot, about $25 to replace, you can get a better one that will go about 60 seconds without water, but without water most likely burned up.

Damage to the tank from gas without water hard to tell.

When charging water system after a drain, I open the pressure relief valve until water comes out in a stream, cuts down on the messy spitting at the faucets.