Lois can die and not be returned, at least not in her own body. If Clark dies, he will be returned as himself and in his own body.
Um, I had a good and logical reason for that - 1. The New Kryptonians would have had no reason to clone Lois, 2. Lois herself chose to transmigrate into that body. 3. Lois and Clark can now be on equal terms in life span.
Also, just in general - Lois is a character that grows and learns and changes. She starts out as a hard-bitten reporter, transforms into a smitten fan-girl when Superman shows up and after time (depending on the writer at DC) morphs into a suitable partner for Superman.
Clark doesn't really change. Once he figures out how to be Superman, he doesn't really grow and maybe that's one of the reasons the show didn't go into the fifth season - Lois had already grown into being capable of being a mother - Clark could not be allowed to grown into a father.
Just my 2 cents.
