The clues are relatively easy to solve.
If you add up the clue lengths of the answers and take it away
from 81 you get 9 letters for the unclued entry.
Once you have solved all the other 21 clues add up all the instances
of the 9 different letters. Whats left is the letters in the unclued entry
anagram this. Once you know what this word is you can immediately
put it in the grid. Then you can start putting the other answers
in the grid using the unsolved minesweeper grid as a guide.
IE You don't have to work out where all the mines are before
you can start entering the answers in the grid.