Unresponsive Pico

The regulator actually has automatic shutdown, so it's almost certainly the diode that's blown (I'd check as @DrAzzy says to make sure though).

If that's the case then you have a few options:

• Replace the diode (any diode will do to get it to work, and they're cheap!)
  
• Short out the diode - potentially easy, but it'll mean you won't be able to power the Espruino from batteries any more. Also if you short the board out with it shorted, something else will end up getting hot!
  
• Replace the diode with a PPTC (self-resetting) fuse. Again, you won't be able to use batteries, but it will at least save you from future problems
  
• Or if you don't want to do any soldering you should still be able to power your board by putting a 5V supply between GND and VCC/5V pins