The following quick and dirty regex will replace:
Code:
<h1>TWO</h1>
<p>TITLE OF CHAPTER</p>
with:
Code:
<h1 title="TITLE OF CHAPTER">TWO<br />
TITLE OF CHAPTER</h1>
Find:
<h1>(.*?)</h1>\s+<p>(.*?)</p>
Replace:
<h1 title="\2">\1<br />\n\2</h1>
It's not perfect, but should save you some editing. (Sigil uses the
title attribute for the toc.)