In "You will end up alone", is "alone" an adjective or an adverb?
I mean, one can say that "alone" modifies the verb "end up" and, therefore, it is an adverb. However, this phrase can also be understood as "You will end up being alone", in which case it would probably be an adjective.
Besides, it's not that you are performing the action of "ending up" and are doing it all by yourself (unlike, say, the action of dancing all by yourself in "You will dance alone", in which "alone" definitely modifies the verb "dance", and, thus, is an adverb); it is rather a resultant state that you finally arrive at in the process of "ending up".
Unlike in the action of dancing alone -- where you start alone, continue alone and finish alone -- in case of the action of ending up alone you may not at all being alone in the very beginning of it:
"Jack, you are so rude with your friends, you're surely ending up alone!"
Jack still has some friends at this stage of the process.
So, taking this perspective, it seems logical to assume that the word "alone" in "You will end up alone" modifies not the action itself (that is, not the verb), but merely the resultant state (that is, the implied gerund "being", which is dropped off from the phrase), and, therefore, "alone" here is an adjective. However, the noun "being" is not found in that phrase. In fact, there are no nouns in that phrase at all!