Yeah I've never been a fan of Superman being straight up immortal. Abnormally long lifespan, sure. I wouldn't mind him living through like three or four generations of Justice Leagues. But straight up immortality? Nah.
That said, I also don't really mind him having another family after Lois and Jon are dead (or even while Jon is still alive, depending on how long his lifespan is). It happens. Sometimes spouses die. Sometimes people move on, whether they planned to or not. Doesn't make his and Lois' relationship any less special. it's just a part of life. And I'm sure Lois and Jon wouldn't want him to be alone, for possibly hundreds of years, after they're gone.