Your old license will work forever, but only for the older version you unlocked, of course. You'll be able to keep playing the older version even if you decide to not unlock the newer version, as each license is "bound" to its version, so if you unlock a license for v1.0.0 and then v1.0.1 comes, you can still keep playing v1.0.0 by using the v1.0.0's license.