1994 Ford Escort BROKEN THERMOSTAT HOUSING Bolt

Ok, I usually do most of the work needed to be done on my cars even though I am a girl and even though I don't always know exactly what I am doing. Everything I know is self taught. I am by no means completely ignorant when it comes to working on a car, but in all honesty I DO ask a lot of questions if I am unsure about what it is I am doing. With THAT being said.
my 1994 Ford Escort Wagon (1.9L engine, 4 cyl, 5 speed manual trans, front wheel drive) has been running hot when stuck in "stop-and-go" traffic so naturally the first thing to check is the thermostat. Well, my last car was stolen about a month ago along with ALL MY TOOLS which were in the trunk, so I sought the help from someone I know, asking to use their tools to do this job. Well, just like a majority of the guys who have been around when I am about to or am working on my car, he felt he needed to do it himself and proceeded to do so before I even got outside. And what usually happens when someone else works on my car instead of me happened. HE SCREWED IT UP! Somehow he managed to get one of the thermostat housing bolts part way unscrewed AND THEN BUSTED IT OFF! So part of the bolt is still in the housing which means that the housing is now loose and has coolant seeping out on a constant basis and when I drive it and the coolant gets warm, it then bubbles out of the spot where its now a little bit lose! Not a lot is coming out in either instance, but it its still coming out! My number 1 question is if this is going to damage my engine at all if I continue to drive it like this? I mean, is my engine taking in air that's going to cause it to malfunction? How damaging and what sort of damage will this cause? Also, any suggestions on how to get the broken bolt removed? Thank you in advance for any and all help that's provided!