outch!
What ESC has that much BEC ?

Sorry to hear, if the BEC on the ESC isn't toast, there may be some hope.
The only bad part would have been if a + or - got into the "sensing" wire on the servo or ESC...

If it were me, I'd get a volt meter & hook to the red & black leads on the ESC receiver connection & check for "normal" voltage 5.5, 5.7, 6volts?

If the ESC tests good, then connect to the receiver (no servo) & test.
If the ESC gets signal, then try the servo...

Like Dave H was saying...
If you really don't trust the receiver, a RX pack & a servo will tell you if the receiver is good, & you can test the servo...
The regulator in the ESC may not take another hit like that if something is still shorted...