Dan was one of the KGB officers working on the Dead Hand project. As such, he was given a necklace similar to Elizabeth's, containing a suicide pill. During the extraction attempt, he is shot by FBI agents, obtaining what looks to be a fatal wound. However, his necklace is shown open, indicating that at some point in the mayhem, he also swallowed its pill.
In November 1987, as he dies in the back of a getaway van, Dan asks Philip to relay messages to both his parents. He expresses his love for his mother and thanks her for her sacrifices. He then says he's glad he never saw his father again, and hopes he dies the miserable death he deserves.
Dan does not appear to have operated with a partner (female or otherwise). He lived in Skokie, IL and ran an accounting business in Chicago. Dan expresses no regrets about his life, saying it was interesting and he got to do what he wanted.