Excel formula keep fixed

Hello I attached a sample Spreadsheet. It has 2 worksheets (Sheet1 and Sheet2).
In Sheet2 It has 3 columns and 3 rows of numbers. On Sheet1 there are formulas that reference the numbers in Sheet2 and add them up. However, I want to know if there is a way that formulas in Sheet1 will not change, even if I delete a column in Sheet2. I need to delete columns in Sheet2 and then I add in another Column later. However, once I delete a column in Sheet2, even if I add a column back in later, the formulas in Sheet1 are showing the Sheet2!#REF error.
The actual sheet I am working on is much more involved then the sample I provided, so when I need to fix the #REF error it is very time consuming process. Thanks for any suggestions on this.