Hmmm. Although we look at a car and say it has XXXXX miles, and she can go for XXXX more...it's not quite that simple. Each component of your car has a service life that depends on a number of factors. Your engine, your transmission, your brakes, your tires, your steering components, etc. At 0 miles on the odometer, everything is at the same point of wear. After about 5k miles, your oil is typically 'worn' and should be replaced - which starts the counter over on your oil. After say, 15k miles, you're due for a new air filter. Those, however, are the rapid consumables.
The slower consumables are the tires, the brakes, the shocks, etc. Eventually those get changed, and their wear starts over. Say you replace your tires at 60k miles or so. At the current mileage, you're probably 23k miles on your fourth set of tires. So, as long as you keep your tires in shape, you won't have a tire issue that stops you.
Now, the major components - engine and transmission - also have their service intervals, but you won't have a definite service interval on replacing the engine or transmission: sometimes they last a long long time, and other times not so much. Re: your question...replacing your transmission won't affect anything on your car, other than the transmission. It just means you shouldn't have a transmission issue again for a (hopefully long) while. Your engine and suspension also have 200k+ miles on them, and replacing the tranny won't affect those one way or the other.
In other words, before you drop the $$$ on a tranny rebuild, get your engine and suspension looked at. If either of those needs major work as well...you should factor that in to your cost. If money's a major consideration, then the last thing you want is to replace the tranny so it can go another 100k-200k miles...and then find out that your engine needs major work.