All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
Whoever died without expiating for an oath, then the amount that is to be paid for expiation has to be deducted from his inheritance before dividing it, in case he left wealth behind. This is what his heirs must do in this life. As for the Hereafter, then, if he was not negligent regarding his oath or he had sincerely repented from it, then he won't be held accountable for that, Allah willing. This is because Allah forgives the one who sincerely repents, as reported in an authentic Hadeeth. However, if he was negligent regarding his oath, then he is like any other Muslim who died without fulfilling the rights of Allah Almighty; if Allah Almighty wills, He forgives him or if He wills, He holds him accountable for that.
Allah Knows best.