Both are correct. One is present and the other is past. "The cake is eaten" (means there is no more cake) "The cake was eaten" (means somebody ate it) "The cake has been eaten" (means that right now, the existence of the cake is a memory) Note that the first and the third assert the same fact. However, they think about that fact in different ways.

Both sentences are correct, but they convey slightly different meanings. "The cake is gone" implies that the cake is not present at the moment of speaking. It suggests a current state of absence. "The cake was gone" implies that the cake was not present at some point in the past. It suggests a past state of absence. So, the choice between the two depends on the context and when you want to convey the absence of the cake.