Contested WIll

Yes, especially if it appears that it was an unintentional oversight to omit the heir in question. This can happen, for example, when there is a child born after the will was executed and the will was so poorly prepared that after-born children were not taken into account. This can also happen, to cite another example, when the testator was not aware of the existence of the heir.  In order effectively to write an heir out of a will, the best practice is to actually write the heir out of the will; in other words, specifically identify the heir, describe the testator's relationship to the heir, and use clear and unambiguous language to the effect that the heir is to receive nothing.  Short of that, an heir is certainly in a position to contest the will.