Okay lets agree to your point once.
Mrs. Basu was living separately. In this situation if a video is released with anti- Basu propoganda Basu can simply tell people that she has lost her senses. He can use his son who would tell everyone that his mother doesn't want him to get married to Kangana.
Or He can easily kill her in an accident and then win simply by sympathy votes.
Or He can get her arrested for defaming him and blamed the opposite party playing dirty games.
Family of course contributes to the good will factor but it cannot stop anyone from contesting. Gandhi family would not have contributed to politics anymore when Mrs. Maneka Gandhi choose BJP over Congress. If this party doesn't give Basu a ticket he can choose some other party. Any other party will readily accept a veteran politician.
At best they could have showed Basu lost the election or should have showed that the Election Commision cancelled his candidature. Instead they showed end of his poltical career. Halwa hai kya ? The people who twisted a confirmed rape case cowed down by a video that only accuses him but doesn't offer any evidence?