The description of an item will tell you the conditions for "enable / disable".
In the case of one Sunblade, a bonus action is required to make the blade appear (dis) and its fall has no direct effect because it is not indicated in the description:
While grabbing the handle, you can use a bonus action to […] make the blade disappear.
However, in the case of one Flame language sword, dropping would have extinguish the flames:
The flames last […] until you drop or sneak the sword.