Don’t arrange songs in a way where you just keep adding layers onto layers. If all you ever do is build up, the music has no dynamics, and the ending can then feel like falling off a cliff. That’s fine here and there, but if every song is like that, it’s simply boring. So, don’t just add, also remove throughout a song. Then the ending can feel as natural as if it were being played by a full band. The whole song and set will also be more fun to listen to from the audience’s perspective.
From my point of view, if you use a looper live, it’s best to do it in a way that doesn’t really sound like looping. Unless you play some kind of dance music, the looper should be a tool to serve the arrangement rather than becoming the defining sound of the performance.
Aside from that, the fadeout doesn’t have to be lame. You can use an expression pedal to control the looper’s volume and use it to crossfade between the loop and your live instrument.