Wifi shows "Hardware not detected" suddenly. Did Apple Diagnostics and confirmed that AirPort card is dead. Called Apple authorised service provider (A.Lab) in Singapore and they quoted me a whopping labor charge of USD $90 and USD $110 for the AirPort card. Since it is just a dead AirPort card, I decided to replace it myself instead of sending to the authorised service provider.
The replacement of the AirPort card was straight forward. Did it in less than 10 minutes and is business as usual.
Be patient when connecting the antennas back to the AirPort card.