I had an 80 Chev truck and broke a tranny line, had an extra quart of tranny fluid that got me off the highway onto a side road. Arranged to get to an Autoparts store and got 2 gallons of tranny fluid and some neopreme hose. Cut the line, installed the hose, clamped it down and refilled the tranny. It was right outside a truck stop with a **********, but I was too busy to go in.
Truck started up, moved OK and I never had an issue with it, even though I use it to launch and recover a 20 foot boat.
I don't know if I was lucky or not, but I had no ill effects from running out of tranny fluid.