When creating a new Soapbox Mailer campaign, one of the key things you'll need to do is select which of the Email Templates you'll want to use for the campaign. The Email Template field is simply a lookup field to the Email Template object, so when you click on the magnifying glass to the right of the Email Template field on the Campaign page, you'll see a pop-up window to help you find the correct Email Template you wish to use.
By default, Salesforce only shows you the most recent Email Templates that you've happened to view. It is very common for this default search result to show no Email Templates. Don't worry, your Email Templates haven't been deleted. Your logged in user just probably has not looked at them recently.
This is expected behavior as a standard Salesforce functionality, and unfortunately, cannot be changed.
There's a simple solution though! To show all your Email Templates, just type in an asterisk in the search box, and click the Go button. Then, you'll see all your Email Templates.