Ask the person who services your tank. They usually have alot of experience in retrieving dropped straws and canes. Sometimes they can fish it out. Sometimes they will empty the tank and pour out the nitrogen and any straws and canes at the bottom, ... if the semen is worth the trouble.
If it is the whole cane you may have problems getting the canisters either in or out. Straws are easy, that's just a empty it deal and fish it out. No hurry with that unless you need that particular semen. Canes can be a problem that needs addressing promptly.