Slipping

The most damage was done by continuing to force the car to move. If that was automatic transmission fluid that was leaking, it could have been as simple as a leaking cooler hose. Once the low fluid prevents one of the clutch packs from applying fully, slippage between the clutch plates will occur. That can result in more wear to those plates than would normally occur in the life of the transmission.

The first thing to do is have the car towed to a repair shop. Trying to drive it there is going to result in a repair bill much larger than the cost of a tow truck. Once the repairs are completed, your mechanic should be able to give an estimate on the amount of life left in the transmission.