If there’s a link to it from somewhere, Google ought to index it and keep it indexed. A quick google returned a discussion suggesting that orphan pages with no incoming links will eventually be de-indexed (assuming the bot had the time to index them before they got orphaned), though it might take a long time. It’s from 2004, though, and Google has revamped their systems plenty of times afterwards.
If there’s a link to it from somewhere, Google ought to index it and keep it indexed. A quick google returned a discussion suggesting that orphan pages with no incoming links will eventually be de-indexed (assuming the bot had the time to index them before they got orphaned), though it might take a long time. It’s from 2004, though, and Google has revamped their systems plenty of times afterwards.