Hi Robert,
As you know MAMP localhost is beyond our support. It's looks that your database lost data "memory".
Joomla nor components cannot delete anything alone. You can check also "Latest Actions" in Joomla Admin what is last action date/time.
Maybe uncle Google can help you more. I can only guess that somebody else had similar issue before, used CMS does't matter, it could be WP as well. Maybe there is shortcut that revert database, who knows!?
I also use localhost software but for PC and never had this kind of issue, I only deleted database ones. Sorry, but this time we cannot help.