If a person has left his estate to another person but that person has since died, who will inherit

Do you mean that the heir died before the person whose will you're talking about? Any reasonably crafted will should specify what happens if an heir predeceases the decedant. Are you sure that the will in this case does not?

But if you mean that the named heir died sometime after the person whose will this is, it depends on how soon after the first death the second death occurred. In many states if an heir dies withnin 120 hours then the deaths are deemed to be simultaneous, and so whatever contingency is defined in the will is followed. But if the heir died more than 120 hours after the first person then he inherits in accordance with the will and now his heirs inherit his estate in accordance with his will.

... Any reasonably crafted will should specify what happens if an heir predeceases the decedant. Are you sure that the will in this case does not? ....

If it doesn't, it would depend upon the statutary law of the state or country where the decedent resided. That would normally contain rules of construction to answer this question.