In Season 5, Will and Lisa ultimately decide not to get married at the altar. OK, that's fine, but why did they not just stay together but not married? Lisa literally disappears in Season 6 and is never even mentioned. Even weirder is the fact that Will's mom Vy marries Lisa's dad at the end of Season 5, but in Season 6 when Vy shows up again, there is zero mention of her husband. Do you think that had Will Smith not agreed to come back for a season 6 they would've had Will and Lisa getting married as the series finale?

The husband wasnt mentioned because that wedding episode was written as the last show of the series.

Lisa has suffered too many love life problems in her own life since after her mother died. So after her father, Fred, and Will's mother, Vy, got forced correctly to get married, Lisa, Vy and Fred moved to New York officially.