Suppose the astronaut died after landing, while on the surface of Mars.

Cremation isn’t desirable; it requires too much energy that the surviving crew needs for other purposes. And burial isn’t a good idea, either. Bacteria and other organisms from the body could contaminate the Martian surface. Instead, the crew would likely preserve the body in a specialized body bag until it could be returned to Earth.

That seems like a silly contradiction. If we are going to mars we are going to contaminate it. We are the invasive species in that case, and we are the life there.

Even probes we have sent haven’t been perfectly sterilized, despite our best efforts.

Returning anything from the surface requires a lot of energy. And if we are there in person doing research we are gonna contaminate things. Would make the most sense to do a burial and call it a day imho.

https://www.space.com/11536-moon-microbe-mystery-solved-apollo-12.html

https://www.nasa.gov/ames/lunar-biology-lab