Project length

Does it stop at the end of the audio or midi clips or does it simply keep going? 

The time line goes way out to the right but the music playback should stop at the end of the longest track. 
I have, in the past, when there was silence in the track simply split it at the end and then selected the right side clip and hit delete. That removed the long silent clip and the playback stopped at the end of the left side clip. 

If you export the song and look at it in an editor, you will see where IT thinks the end of the song is. If it thinks the song ends way to the right of the last note.... you will see the wave end and a straight line finishes the time in the song. 

There most likely is a command or a global setting to stop at the end.... I don't know why most people wouldn't want to stop at the end of the last clip in a project.

Look in the global and project settings tabs to see if there is something in there relating to the end of a project and stopping the time line. 

So far, all my DAW's from MC4 to X1 all stop automatically at the end of the longest track and reset to the NOW marker on the time line.  

I've never had to reset that feature, so therefore I never went looking to find out where the settings are hiding.  That's where I'd start looking or hit F1 and search for it.