Unfortunately, I haven’t found any way to get your saves back once they’re gone. This has happened to me about 3 times now, it’s really annoying but if you have them saved as images or text it’s less so. From now on, whenever you save a character, save a backup as text so you don’t lose them all again next time. That’s all, sorry.
Sorry to hear about the loss of your characters. Heromachine saves your characters as a .sol file, that while are not truly cookies are treated like them by your browser. Jeff has posted somewhere in his blog posts to find where these files are stored and I’d have to go search for it to tell you where that would be. As Kaylin has pointed out you should save your characters text string to a word file. click save, click on the text tab and copy all the text in the window into your favorite word processing program . To work on the character to click load, click the text tab and paste the text string back into the window. The Advantage to saving your character this way is that so long as you have access to the text file ( flash drive, online cloud storage, etc. ) you can load and work on them from any computer.