WHERE the oil leak is would determine how bad it could get. There are some simple things that could cause it. One that's irritating is when the drain plug is leaking. Some vehicles have a washer of sorts made of tough rubber that, when it breaks down, will leak. Sometimes, its from the drain plug, which is actually a bolt, getting cross-threaded, in which case it requires replacement.
Another easy-to-fix problem is gaskets. There's a gasket on the oil pan that is, in most cases, pretty easy to replace. The valve covers could be the problem, but in Toyota Corollas, depending on the year, wouldn't have that problem.
If the head is where it's losing oil (under the throttle body-- fuel injection) then you have your work cut out for you and it needs done by a professional. Also, if the head gasket is blown or the head itself is cracked, that's bad juju. Oil could be seeping into the water or the gas (it will smoke if it's doing this).
As long as you check your oil often, keep the oil level up between oil changes and don't let it get low, you could go awhile with the leak without doing any damage. Check your oil and find out how fast a leak it has and then you'll know how often you will need to add some.
Another interesting thing about leaks. I had a vehicle that leaked around the drain plug every so often. I found out that it was when the oil had started breaking down that it was thin enough to leak. If I didn't go past the time to change the oil, it wouldn't leak, so when it started leaking, I knew it was time to change it and POOF! leak was gone. That actually was beneficial, as I didn't have to keep tabs on my mileage to change the oil!
Toyota Corollas tend to be good cars. They run for quite some time, as far as mileage. While their parts can get a little more expensive, in the long run, since you won't have to replace them as often, you'll come out ahead. Good luck. Keep tabs on that oil.