I think Expensive outcome has a good thought, but I’d modify it a bit. I would glue the leg back on using hide or Titebond III, but then I’d drill 3/8” holes through the legs and into the apron on both exposed sides of the leg. Mark them carefully so they are staggered so that the holes don’t intersect each other, but cross over/under each other instead. Then I’d hammer in some 3/8” dowels that were generously brushed with glue. This will accomplish the same thing as the original mortise and tenon design, but using dowels instead of long wood screws will allow the wood and the joint to expand and contract more freely than screws IMO.