"If that's what was done - opening a song - then that's an action that cannot be undone; this isn't only true for BB, it's true for basically any software I've ever used."
That is not entirely true. "Any program" would open a "second, third, etc." (song/document) without affecting original. That's the reality.
Many programs, but far from
all, and it doesn't look to be the standard in the audio industry. Pro Tools, Cakewalk, Performer, and Studio One don't do that - you have to close one project to open another, and none allow for multiple instances. Reaper doesn't by default either, unless you manually open a new tab before opening a second project. FL Studio allows for multiple instances, but it looks like opening a song will close the existing one by default. The only other DAW that I know of which lets you have multiple projects open in separate windows is Logic, which prompts you whether to keep the existing song open or not.
By comparison, BIAB supports multiple instances, so you can have as many BB songs open as your computer can handle, and you can copy/paste
some things between them - though to create a second instance you either need to manually open one before opening a song (same as in Reaper and FL), or open a song file from outside of BB. Like in Reaper (and likely many other programs), opening a song file from within an existing instance assumes you want it opened in that instance.
If anything destructive is being done to the project - warning is usually displayed. That's how most programs that I am aware of function.
And at least in the most common ways, that's how BB works - if you close the song without saving, or open a new song with the current one unsaved, BB will prompt you. As mentioned in this thread though, there certainly are things that don't have a warning, like changing the style - and I'll certainly lean on the devs to have that one corrected.