Event Change code to protect formula if data entered manually

I have a worksheet for formation evaluation that automatically inputs the "Top depth" based on the "bottom depth" of the previous formation. However, there are instances where the top depth needs to be manually entered, thus deleting the formula. I would like to keep this flexibility, but have it so the initial formula is retained and automatically input if the manual entry is deleted or the spreadsheet is used for another evaluation. Obviously I could just delete and scroll the formula above it down to cover, but I believe there is a way to write a VBA code to ID the event change and repopulate the deleted cell with the formula. Is this possible?

OK I think I attached correctly, sorry, I am noob to the forum.

Anyway, I have a formula is column "c" which automatically populates the next "top depth" based on the previous "bottom depth", and if it's a new wellbore (sidetrack) it puts is a "0" as the new start point.

I want to be able to leave column "c" available for manual input if need be (say if certain formation info is missing, or there is a gap in info that would require some footage to be skipped, etc.), but if the manual entry is deleted then it auto-populates the cell with the formula again.

Thanks for the help

Thanks Solus-

When I copied your code over to my worksheet I noticed it doesn't revert back right away, you have to highlight the cell again for it to fill in (when I delete a manually entered number into "c#" and hit enter it stays blank, but when I select that cell again it auto-fills. Is this something I did wrong in copying over the code? Otherwise works great, and I did not notice this with the worksheet you attached, it fills in right away.

OK nevermind I think I got it, I did not copy the "option explicit" over and just did the stuff in the middle. Seems to be working great now. Couldn't have done this myself so thank you very much.