I've seen epubs with the TOC at the front, and then each chapter title has a link back to the TOC page. Would that work for you? You could also put "The End" at the very last page and link it back to the TOC as well. Not sure how to edit mobi files directly, but if you changed the epub in Sigil to link back to the TOC as I said, then just convert it to mobi, the links will stay (I know I've done it, but I'll have to look through my books to even find which ones had the links back to the TOC if you need examples of the code).
Edit: Here's a sample:
This links from the TOC page to the final "Epilogue", kept as created by Sigil:
This links from the final "Epilogue" title back to the TOC at the front of the book, this keeps the title as a header:
<h4 class="sgc-toc-level-1 sgc-6"><a href="../Text/TOC.html#sigil_toc_id_52">EPILOGUE</a></h4>
Just remember to give it a new ID# that hasn't already been used. Here I assigned 52 since 51 was the last used number for Epilogue.
You could probably just stick another TOC at the back of the book if you'd prefer, just copy the TOC.html contents into a new file but name it TOC2.html.