1998 Ford Taurus How long can the cat last

I am looking at over $1200 to fix the engine and then there is no guarntee that it won't still have issues. I bought the car at an goodwill auto auction back in July for $450 and use it just to drive around town. It is getting about 20 mpg right now with no operational issues except what happens when you have a misfire. I live in a state with no inspections so I could be bellowing black fumes from my tailpipe and no one would care. I am just going to drive this car till either the engine goes or the cat stops it from working, donate back to Goodwill and go buy another car.

In Indiana they don't care what the car is like, as long as you have insurance you are good to go. The misfire is due to the car overheating at somepoint and causing the exahust valve to become burnt and damaged.

I had a compression test done and a leak down test done which showed air coming out the tailpipe and the radiator resivor.

Won't unpluging the fuel injector cause the computer to sense that and in turn increase the fuel flow through the other 5 injectors which would cause even more unburnt fuel to get to the cat and have all the cylinders misfiring? The reason I ask is this is the one question I can't seem to find any kind of concesses on. I have been told by a few people that the car's computer will sense the misfire and shut off gas to the misfiring cylinder, others have scoffed at that and said if I unplug it more fuel will go to the other cylinders making the matter worse and others like yourself advising to unplug the fuel injector. All the opinions I have gotten was that unburnt fuel will damage the cat, but I can't get agreement on how I can lessen that damage.

Why is this such a tough issue to address?

How do you unplug the No. 1 fuel injector? Also what would cause the head to crack farther? What signs should I keep an eye out for?