Looking at this problem for extracting cells from excel formulas, this could be a valid solution.

For sheet names where you use only any word character (\w) than you don't need apostrophe (') before and after the sheet name (Sheet1! or Sheet_1!).

For sheet name where you use any non-word character (\W\w) than you need apostrophe (') before and after the sheet name ('Sheet 1'! or 'Sheet.1'!).

sheet = ('[^']+'|\w+)!
cell = \$?[a-zA-Z]{1,3}\$?[1-9]{1,7}(:\$?[a-zA-Z]{1,3}\$?[1-9]{1,7})?