If there is shade in a crease or the underside, they will survive.
Mattress does not conduct heat and is a insulator.
My parents executed that procedure in summer when temps routinely reached over 100F in western India. We had a flat roof on 3rd floor of house. I used to watch the bedbugs come flying out of the mattresses. Even the bug eggs died in the heat. Then we would enjoy several months of bed-bugs free beds.