1991 Mercury Topaz transmission failure

My daughters 91 Topaz made a loud bang then coasted to a stop. The motor ran fine but when shifted into any gear it just made a faint whirring sound. I thought it might be the drive axel so I raised the car to test it. The right front wheel could not be rotated with the car in park but would turn in all other gears. The axle feels solid and has not pulled out of the tranny. Any suggestions other than replacing the transmission?