BuddyPress.org

I think you’ll find it does exist and is how plugins are meant to work by first checking that BP is loaded?

It might be easier if you explained what you’re trying to achieve rather than the approach you would like to take to achieving it, then someone will be able to, possibly, provide an alternative method to achieving your requirement. It’s possibly a slightly confusing request as surely with BP not activated, no BP theme running why would any WP theme files need to be checking to see if BP is running?