^Right. There are already things that can be done to extend a woman's fertile years, and that's bound to be a lot easier than arranging for two different species to produce a viable offspring. Saavik is clearly still in her reproductive prime when she marries Spock in 2344, based on the precedents we have of other Vulcan females, but even decades later, if menopause set in, there would be medical means to delay or reverse it.
And note I said "if." We don't even know if menopause exists in Vulcans.