So ...

Upon activation, go to Users => Capabilities.

This is the page where you can load any Wordpress user role and change its capabilities and permissions:

You'll see an overwhelming array of options, but don't worry, it's easier than you think ...

As a first step, you'll have to load the Author user role capabilities (by default, the plugin displays the Subscriber capabilities). Locate the "Select Role to View/Edit" panel in the top right corner of the page, and select the Author user role from the drop-down menu:

Then, click the "Load" button to load the Author user role capabilities.

Now locate the "Deletion Capabilities" section and simply uncheck the box next to "Delete" and/or "Delete published" (posts):

And that's it! Just don't forget to click the "Save Changes" button ... Now, users with the author user role will no longer be able to delete their posts.

OK. Now let's see some closing thoughts ...