.MHT is HTML embedded in email
File Juicer 4.2 can extract HTML and images from MHT files. You need only enable the email attachment in the preferences as MHT is uses an an email file format too.
The only requirement is that they have the .mht extension so it can apply the stripping of the specially encoded characters in to convert it to HTML.
Converting MHT files with Automator
File Juicer comes with an Automator Action for converson of MHT files. This will let you be able to combine File Juicer with other actions. The result of the Automator action is the folders for each mht file. Inside this folder index.html files link to the first HTML file extracted from the MHT archive.