'99 Plymouth Neon coolant leak, car won't start?

My friend and I were driving today in his 1999 Plymouth Neon when we heard what sounded like something dragging under the car after he went over a set of railroad tracks. You could hear whatever it was catching wind and making a whistle noise. He pulled over to look under the car but the sound stopped a HUGE pool of coolant started leaking out. He said his car was overheating the other day and he put coolant in it and it was fine. We tried to get home immediately but, once again upon going over the same railroad tracks, his car overheated to the max and shut off. It's obvious something happened with the coolant system but he's afraid that he messed up his engine. It will make noise but not turn over. Could it be a blown head gasket, or maybe a hose that burst? What are the chances of this messing up his engine? His car is at a mechanics right now but they're closed and I'm just trying to give my friend peace of mind. Than