Moral framings like this are pointless. That's a scenario that's never going to happen, so why worry about it? Instead, we have a real question to ask:
Which of these would you choose?
A. Have children and be less happy, more stressed, and have less money and less free time for your a ~25 year stretch somewhere between ages 20 and 60.
B. Don't have children, be less happy, poorer, much busier, and more stressed during those years, but potentially more happy in your old age.
The point is the realization that happiness is not the most essential thing in thing. My hypothetical is meant to be similar to the choice between two futures, one, where you have one more loved one and maybe less happiness, and the other where you have one fewer loved one and maybe more happiness - i.e the choice to have a child or not.
Happiness is a kind of short term thing. Life has better things to offer in my view.
If you could choose between a future where your happiness doubled but one of your loved ones died, or the unadjusted future, which would you prefer?