[Mithalwen]

I don't know that Denethor would have withheld the crown if Aragorn had the support of the nobles especially his heir and Imrahil. As soon as Denethor died they would cede authority anyway. I shuspect that the sensee of honour that meant the stewards did not claim kingship would have held in the end. However I suspect for Denethor hope and despair really were akin and he could no more cope with a victory forseen as defeat. I suspect he would have taken the same route out.