It gets very weird. Some models say that going outside of the observable bubble is the same as passing the event horizon of a black hole. When you are in a spaceship and you pass the event horizon of a black hole, nothing happens to you yet. The event horizon is not some kind of physical barrier; you can pass it without even noticing that you passed it, though of course when you are past it there is no turning back. From the outside perspective however, there is a problem because information is conserved. According to some theories that information will be radiated out. So from the outside perspective the spaceship has been completely destroyed and radiated out. From the inside perspective the spaceship is happily orbiting. Something similar may happen when a spaceship leaves our bubble. Of course these models may be wrong, but it shows that the question of whether the spaceship still exists is not very clear, and may depend on who you ask. So is it ethical or not? I'd say yes because from their perspective nothing happens, well, from their perspective we die and burn. Note that in QM it's clearer: if you are the one that sees the dead cat, then for all practical purposes it's truly irrelevant whether the one that sees the alive cat exists -- there is no information being radiated back or something else that indicates that that version exists or not. The predictions of MW and copenhagen are identical, whereas with black holes we could observe whether something is being radiated out or not, and we could drop ourselves into a black hole to see what happens.