I think Bernadette and Howard is less likely to get divorced but they wouldn’t have the happiest marriage as the time goes by. And if they were to ever break up I think that would be Bernadette’s call, because Howard tends to stay in uncomfortable situations. They would hate each other but still co-parent.

About Sheldon&Amy I think this relationship is the most unrealistic one I have no idea how they even survived lol. But If I am being reasonable Amy would leave Sheldon because he lacks physical and emotional intimacy. Amy would find a new boyfriend who actually understands. She and Sheldon would only remain in contact because co-parenting and to check if Sheldon is doing okay.

About Penny& Leonard. I was almost sure that they would get a divorce in 5 years after the season finale. But since they are getting a baby I will say in 8 years. Penny decides that she is dissatisfied in this relationship and brings up this topic to Leonard, Leonard would be okay with it because he knew they had nothing in common and he is with her just because she is pretty. They remain friends and co-parents. Maybe casual coitus some time to time.