Do people look same after they die and when they sleep?

Depends on the way the person died as well. If they died peacefully yes theyd look like they're sleeping but if they died a more violent death its different

No. That is one reason I refuse to look at people on display in a casket, even if they are family members. I prefer to remember how they looked when alive.

I've only seen one dead body, and she looked the same as when she slept.

they look like an empty shell and the face becomes pale/greyish ..

Definitely...when dead no expression.

No