Death in this instance puts a limiting factor on the example. If the statement said that Ms Smith was unmarried until she married Mr. Jones then that would indicate that at some point she did get married. It does not specify when she was married only that she was no longer unmarried.
Um, it specifies exactly when she ceased being unmarried.
Just like the sentence "they had no relations until she had given birth" must mean they had relations immediately after the birth. If you want to read this as an affirmation of their having relations, as opposed to a statement of her virginity before the birth.
The verse is meant to convey that she was virginal prior to Jesus' birth. That is all.
SD