IIRC, Sarah was completely rejuvenated in order to give birth to Itzhak, but I don't remember that G-d took it back after he was born.
Apparently, Avraham was eager to have more kids in his old age.
Why Sarah didn't have more kids with Avraham?
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Maybe Sarah did have more children with Abraham. The Torah says:
"-V'Avraham zaken ba bayyamim, v'Hashem berach et Avraham bakol -- And Abraham was old, and well advanced in days, and the Lord had blessed Abraham with everything." [Gen. 24:1]
The Talmud asks: What is meant by 'with everything' [bakol]? In the fact that he had a daughter and her name was Bakol. [Bava Batra 16b]
Later in that tractate, the Talmud says that all one may infer is that the All Merciful did not deprive Abraham even of daughter. [Bava Batra 141a] In other words, you can't say you have everything unless you have a daughter!
In fact, didn't Hillel say: To fulfill the commandment to be fruitful and multiply, you must get married and have a boy and a girl? [Yevamot 6:6]
Sarah having a single child at 90 was a supernatural miracle. Having multiple children afterwards would have been multiple supernatural miracles. Since G-D already 'accomplished His mission' of continuing Abraham's progeny through Sarah with that one miracle, there was no need for Him to continue doing miracles by giving Sarah more children.