Youtube will detect the music that's in your video, and then will look it up and do what the owners of the music want done.

They might disable your video unless you remove the entire audio track. (You can't just remove the song and leave the audio track, of course.)

They might allow it to be up, but put ads next to it.

They might allow it to be up, and just put a little button to buy the music in question below it.

They might (in addition to something above) limit your video somehow -- not let it play in certain countries, not allow it on mobile devices, etc. This limitation will go away if you delete the audio track, however.

They might do nothing.

In any event, I don't think you'll get in any trouble under any of these scenarios, as long as you're posting your video with somebody else's music. (There are other things you can post that can get you in trouble, but this really isn't one of those things.)

Also, it may take a while for them to detect the music. They usually detect it within a few hours, but they might months from now.