I agree. "... is gone" might be shown as the correct answer in a dictionary but I am sure people would raise an eyebrow if you said that in most parts of England!
I would say " has gone" or, more likely "is missing"
This is one of those Duolingo examples where the translations are just not comfortable to English speakers. One (I can't remember which) seems to have created quite a fractious discussion. Sometimes I feel Duolingo needs to allow the more idiomatic responses but I guess that sticking with a rigid dictionary definition means you can avoid debates between English speakers of different backgrounds!
Haha, that would hardly be surprising on a planet where turtles are blue, someone can look like a crepe, you live in an apple, ducks speak english and cook rabbit, birds read the paper, a cat gives a woman a skirt, the cheese introduces itself, children write on a shark, babies take over or it's raining men! Long live Duolingo!!