Use VBA to insert cross references by looping through entire document from insertion point to end

[Guessed]

What is the cross-reference anchor text showing? If it is a cross-reference, that would imply that the words "Click to Return to Table of Contents" need to appear at the top of the TOC. A hyperlink is more flexible in that it doesn't need to be the same words as the location it is pointing to. If your hyperlinks are breaking, it is likely that your TOC field is being updated as part of the save and that the bookmarked range is inside the TOC field instead of being placed immediately in front of the TOC.

Paul's suggestion of using Find and Replace to create the multitude of links is by far the easiest way to do what you are asking for.

Placing these links all over the document for the express purpose of being able to bounce back to the TOC is not as quick as using the GoBack keyboard command. I would recommend you also teach users to press Alt-Left Arrow to return to the last clicked hyperlink.