As you will have found out, if you could not disconnect the fuse, switch or battery it would just keep going until the battery went flat (and damaged) or the switch dried out.
You need to dry the switch out some how. A water dispersal spray may work if you can get it to go into the switch like the water got in there in the first place. As the switch is relatively deep/big I doubt a hair dryer would help.
You are now stuck trying to recharge the 12V battery with an external charger as it will not charge from the on-board charger as that requires 12.2V to be present before the relays cut in. Then seeing if the switch has dried and will switch off. You may need a new switch and 12V battery.