If I had to guess, you had a cold solder joint somewhere, which worked for a while, but then cracked and maybe some stray metal fell and shorted something important.
You should replace the entire board. After a major failure like this, it's more work than it's worth to determine which transistors (and even passive components) survived.
Chin up! Everyone here has fried many many boards. You didn't get hurt, so that's a win!