I have a book that has a page on repairing veneer, "Decorative Wood Finishes" by Annie Sloan. I will paraphrase...to restick veneer, cover loose veneer with brown paper and press down on it with a hot iron until old glue backing is sufficiently heated and the 2 side stick...to fix a gap, use hard sealing wax in a color slightly darker than the wood. First rub in a little wax with steel wool into the surface to protect it. Using lighter, melt sealing wax stick directly over gap. Use palette knife to press hot wax into gaps. Buff to good shine.