Possibly - but it will depend on the exact wording of the will. If it hasn't envisaged this situation and made provision for it it will have been badly worded.
The other possibility is that the bequester will have been regarded as having given directions for only half his estate and the other half will be dealt with under the laws of intestacy.
It will also depend on who the beneficiaries are. If the deceased beneficiary is a child of the testator, there is a provision which means that their children will inherit, unless there is a contrary intention in the will. Dzug is right, it depends on the precise wording of the will.
when I draw up a will, and leave A and B as heirs, then I can use words to make sure that if B dies, B's half goes in equal parts (per stirpes I think) to B's children