You might consider using a 1/4" wood dowel glued in or a 1/4" metal rod epoxied in. Clamp supports onto the playfield to straighten it then with a long bit carefully drill hole in the end grain of the playfield next to and parallel to notch for switch wire. Another method would be to secure a 1/4 or 3/16" metal plate to the underside, this would lower the switch which would require bending the switch wire to adjust it. Just some ideas to fix the break in the plywood.