Whilst I am convinced that actually both died eventually, as all mankind does, I actually believe that you have made some mistake in your comprehension of this play. During the course of the play as Shakespeare relates it to us, neither of these characters dies. They certainly do both have massive changes in terms of their role, as Jessica elopes with Lorenzo, leaving her father Shylock, stealing his money and converting to Christianity, and the lovers take refuge on the island of Belmont. However, at no stage does the play inform us that either character dies during the course of the action of the play. They are one of the happy couples, along with Bassanio and Portia, and Nerissa and Gratiano, that live to tell the tale of this play and presumably live happily ever after.