No one can really tell what will happen. Technically you need to start from the beginning with a drawing, file for permits and get plumbing, electrical and building inspections to determine if the work was done to code(current code). If the inspections are fine and the inspectors sign off then you can probably close before you get the final certificate of occupancy. That is what should be done. However if the appraiser doesn't catch the addition, or the title company doesn't catch it from the survey inspection or the banks attorney doesn't catch it when all the documents are compared then maybe you will get by. But don't count on it. You don't want to sell your home and not be able to close. Find a reputable general contractor to take a look at the addition and give you their opinion of whether it will pass inspections. After that you can have the GC do all the work(drawing, permits, inspection appointments). If you don't pass any of the inspections you can ask the GC to do any of the necessary work. Good luck!
Century21 Yve R.E.
Licensed R.E. Agent
NYS Certified Residential Appraiser