It may endure forever. Conveyance created a life estate otherwise. A potential heir has no interest in a fee simple until the death of the freeholder. An heir is someone who survives the decedent and is designated as an intestate successor by statute. Issue is synonymous with descendants.
Issue includes both children and further descendants.
Distribution is made per stirpes . If the decedent leaves issue, they take to exclusion of all others. By statute, parents usually take if there is no issue. Only take if no issue or ancestor. Fee Tail Can potentially endure forever, but automatically ceases if and when the first grantee of the estate ceases to have any lineal descendants.