What happens if one of your parent sims dies but not the other? Is the challenge over?
Not necessarily. Your surviving Sim can still adopt, use the wishing well, and get abducted.
Technically, as the rules are written, it never specifies that the starting couple need to try for baby
with each other. Instead, it simply says, "Each parent has to complete a new aspiration before trying for baby, adopting, and/or wishing for a child at the Wishing Well." That being the case, it would see the remaining parent could still try for baby, just not with their original partner. Am I reading that correctly, or is there something else in the rules that I missed which would negate that?
Disclaimer: My hyperbole is merely my own thoughts and should
not be read as solid logic for anyone's attempts at the dynasty. Only rulings by the mods are official.