Hi David, best practice would be to find a more reliable computer to trade on or vps. Crashes should be very rare and you should turn off automatic updates and do them manually on the weekend when the market is closed.
This is not an issue I ever have but in this instance what you could do is run the metatrader backtester and see if the trade would still be open or closed and take appropriate action to remain in accordance with how the EA would have traded if no interruption occurred.
If there is a trade open with the magic number of an EA that has auto trading enabled then the EA will manage that trade according to its rules. Im sure you can easily confirm that with a quick test also.