The film would still have been a blockbuster but Jai's death kind of made it more genuine. And if Jai had had a happy ending, the ending would not have been impactful not because a widow got remarried but for the fact that it was the tragic climax that gave movie the real boost and made it what it was. The emotions during and after Jai's death were so high and real. The expressions on Dharmendra's face when Jai was lying in his arms is what made the climax what it was.
So yeah, movie would still have worked but climax would not have been that powerful had Jai not died and got a happily ever after. And it most definitely would not be because of a Widow getting another chance at life, getting married.
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