I fear you are, hosed that is.. that shouldn't happen though, and i gave a suggestion for this eons ago, so maybe it will be fixed in the future, i hope so at least.
Generally if you have direct neighbours IV class and a bad AI combination that can mean you get core ships as raiders, a game ending situation indeed. Unless you have choosen eye bots i guess. then you could try to destroy their warp-gates as fast as possible and just pray they don't attack..
That all said, a IV world is a huge road block, one impossible to tackle in the start phase