Cannot delete buried pipes without digging them back up.

It is heartbreaking as heck to accidentally delete buried pipes after their are covered. Simply make it so buried pipes cannot be upgraded, deleted or tied into without digging back up the relevant sections.

technically you can just start above ground

More likely just some settings on pipes (or any other building) forcing another dialog if you are realy sure to delete that (with option to only delete buildings without that settings). Or it could prevent deconstruction without dialog (forcing you to disable that option first).

that is what auto-save and INTENTIONAL saves are.
save your work before doing any risky editing/building. use a temp file to try an idea.
and pay attention to what you click on.

Could be easily solved by adding a pop up confirmation window when deleting buried pipes.