And Joshua set up twelve stones in the midst of the Jordan, in the place where the feet of the priests bearing the ark of the covenant had stood; and they are there to this day.
Joshua 4:9

The active memorials commanded in Torah were given to remind us and future generations of what God has done for us. Although physical memorials like the one Joshua set up in Joshua 4:5-9 eventually fall (the stones must have been very large to withstand the spring floods year after year, but they aren't there now), it isn't possible to "fulfill" a calendrical memorial, such as Passover and Sukkot, so that it is no longer necessary, unless we no longer need to remember God's love and direction.