Hi, templates are manageable from the Newsletters panel, on top there is a menu entry to access the template list.
The deletion of the plugin does not delete your data, config or templates: this behavior is too dangerous, generally. It’s a design choice, otherwise an unwanted deletion can destroy precious data (newsletters, subscribers, and so one, it’s not only a set of configurations that risk to get lost).
About the tables, if you need to manage them directly they are all the ones starting with wp_newsletter*.