Are all previous expiations nullified merely by the aforementioned person getting married and doing what was sworn to be abandoned, and must they be redone?

The expiations you have performed cannot be nullified by your oath that something will occur, or be done, or be left undone. For an act of worship, once completed, cannot be nullified by consensus. Therefore, do not repeat the expiations you have already performed if the condition upon which you made your oath (leading to the expiation) comes to pass. However, you are liable for an expiation for breaking an oath if the condition upon which you made your oath by Allah to nullify the expiations you had previously performed comes to pass, because their nullification is impossible. And swearing an oath upon an impossible matter necessitates an immediate expiation due to the impossibility of fulfilling it.