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?
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.