Only a big power-efficient chip like M2 Ultra could survive if it could _only_ radiate from one side of the wafer into CMB.
The rest of the silicon will become molten at 100% TDP: H100, Xeon, Core, EPYC, Ryzen.
Most would be over 400C at 1% TDP.
Conduction and convection are linear or close and are effective at desirable temperatures, whereas thermal radiation is quartic and highly convex.
I recall some sci fi like The Expanse where it’s mentioned as an aside that big industrial processes happen on asteroids or moons because you can use a big cold rock as a heat sink.