Only if they're conscious of the simulation.

Number one tell no one, number 2...

Only if they have a consciousness.

The ethics which we use today evolved out of practical ethics - that is to say, it's evolved out of a need for a set of rules meant to be applied in order dictate the conduct of humans amongst one another. Because of this, I think most ethical frames of reference are ill-suited for trying to answer this question soundly.

It seems analogous to trying to apply traditional physics to a quantum reference frame. It's outside traditional Physics's wheelhouse. A different set of tools likely needs to be applied, which has a different starting paradigm.

That being said, your answer is really going depend on what this new ethic's paradigm is, which is arguably completely arbitrary in this specific case.

If you are a human, human ethics of not killing "alive" stuff still applies to you no?

Thinking more into rules of ethics, if those simulated beings came up with their own morals like "don't try calculating all digits of pi in large groups because it causes lag" that would not really apply to you.

Basically different beings have different rules of ethics IMO and you can't simply end the simulation more so because you are a human than anything.

The answer could change in same exact scenario if you are some kind of eldritch being instead of human.

I'd imagine there could be an ethical way to do so through a sunset protocol similar to the concept of rapture (the religious kind, not the Bioshock city) - freeze simulation, move all the beings' minds to "heaven", shut down physical universe simulation (lowering operation costs by at least five orders of magnitude, I'd imagine), and let them enjoy afterlife until they get tired of existing, reach nirvana, or something like that.

That reminds me, I should really get back into AI research.

only way to know would be to enter the simulation and see for yourself.. wait a minute..

If they're sentient? Yep.

We can probably simulate a snail but me killing that wouldn't make my wife scream at me for killing a snail.