Extracts for whatever reason won't ferment as complete as all grain batches. Your beer will be sweet, but it won't be undrinkable by any means. Barring infection, if you don't like it, I'll pay for the postage.
You can add some yeast and see if it does something. There's so little left to do it's not going to do much to flavor so it's really your choice.
It's a tough pill to swallow because you feel like a failure or whatever if your yeasts act like a giant vagina, but RDWHAHB and just drink 50% more than you normally would and you'll still get drunk.