If you use only functions to control stuff that needs actuators in module execution (pyhton controler on module execution). This ‘issue’ does not occur. So, it might, as SolarLune pointed out, better design to avoid classes in this situations.
If you know your game environment will change (doe to scene switching) it is a good idea to check if a references is still valid. Have a look for the invalid attribute.
If you really want to use references to scene data (e.g. game objects) outside the scene, make sure to update the references after a scene switch. If you implement a save/load system you will see how important that is.
Maybe thats why you dont see as many projects that use multiple scenes (levels) projects in tutorials.
How would you reload the char when you switch scenes?
Cause, even using simple functions (no classes at all) I still lose the reference to the actuators. I think since the reference to the original character .blend file is the same for both scenes, when you end the object by switching scenes you lose the reference for actuators for the second scene as well. So, I guess there should be a way to free the first reference than reload it on the second scene.
So if you were making a game that you needed to switch scenes, how wold you deal with this issue? I think my aproach may be just plain wrong