If the engine ran fine....then the ecu was obviously alive at that point.
It would seem very unlikely the ecu just died sitting there whilst doing nothing. Whether whatever was done was deliberate or accidental...something was done to kill it ( if it is dead )
Could be a bad jump start, crossed leads, perhaps some welding on the vehicle ( although I've welded on cars before without unplugging the ecu without harm ) etc etc
But if you follow the basic tests asked...that will yield info.
And you also have not stated when asked, what lead and method of connection to the ecu are you using ? And have you done something odd like left the flash switch "on" on the lead if it is present ?
Is the comms lead always connected to the ecu when you are trying to get it running ?