Can a short-circuited heat bed be salvaged?
What happend was short circuit of course. There is no doubt you overheated HB so copper detached from HB base plate. Because you wrote it doesn't work it means copper tracks are broken.

There is very low chance to fix it. I mean it - near to zero.

What you could do is:


Detach HB from arduino
Find a place where track is broken (which needs to uncover it from protective layer)
Connect it with a wire


Unfortunately even if you do it and your HB will work (electrically) your fixed HB which won't be flat anymore.

So definitely it's to be thrown away.

[edit]

I just realised you have double power HB, which means your HB has 2 heaters... which gives a bit hope.

take a look here



here is schematics which could give you an idea

You could check if your second heater works ok

If yes then you are salvaged! :)

[edit2]
I really suppose the schematics of HB is more or less like this



So if H1 is broken there is a chance to use H2 connecting pins respectively