Marrying a Deceased Woman
Scholars mention that if one dreams of marrying a deceased woman and consummating the marriage, it might indicate his success in achieving a forgotten or hopeless matter, and this success is proportional to the woman's beauty. If a woman dreams that a deceased man married her and consummated the marriage, it might signify a decrease in her wealth, a change in her situation, and the dispersal of her affairs, and it might indicate her death if the consummation was in an unknown house of the deceased. It is also mentioned that a married man marrying another woman indicates gaining authority.
Per Ibn Sirin's Muntakhab al-Kalam fi Tafsir al-Ahlam