It is nearly impossible for you to be deprived of your spellcasting focus. If your focus is lost, taken from you, disarmed, locked in a chest, on another plane of existence, or in any other way parted from your person, you may use your Short action to teleport it back to an empty hand. If your focus is Destroyed, however, you cannot summon a replacement; you must purchase or Craft a replacement, and then sleep with it overnight to attune it. (The new focus does not count as such until after your next Long Rest.)
If you do not have a free hand, you cannot use this ability.