The plugin won't "fall into a loop," no. Again, this completely depends on the settings you're using in the widget(s) and elsewhere on the site. if you're not limiting the number of posts returned, or returning a very large number of posts, or using many FPWs you will indeed run into issues. Again, this would be true of any code/plugin/function that scans a large DB for posts. It's not a FPW issue exactly, rather your specific use is running into a common issue with large post tables.
On the flip side, I'm using several instances of FPW on a site with about 1.5 million post records and about 3 million post meta records without issue. It really comes down to configuration. FPW is intentionally designed to allow advanced users vast control over what is queried & returned. This will always leave room for queries that are unsafe/not ideal for large datasets.