Extension leads like the one you describe, should not be used for high power devices (heaters) unless they are fully unwound. Otherwise what you've described can happen, basically the cables get too hot and melt (potentially very dangerous). Normally the extension leads like this have this written on them, that they should be unwound. Once it started melting probably the trip switch for the stage went, this is in the lobby and just needs to be flipped back.
Heaters consume really large amounts of power and should only be plugged directly into mains sockets, generally speaking they should never be used on extension leads or power bars. And they should not share extension leads.
Please make sure this is thrown away!
Glad everyone is ok
Maybe it could work? But it will be a kaleidoscopic blend of mysterious shadows and rainbow hued-dreams seen through compassionate tears.