Whether this is likely or not isn't really relevant to you. Sometimes these friendships do continue after school/college, and other times they don't. There are, however, two points that I do think are important to make.
The first is that maintaining any friendship requires a degree of effort. It doesn't really matter at all whether you're introverted or extroverted. What matters is that one of you, or one member of a group, makes that effort to send a message or make plans. The way friendships end for the most part is that that just stops happening. It's often not a conscious choice.
The second, however, is not only that friendships do naturally come and go, and strengthen or weaken or over time, but that you can also be in direct contact relatively infrequently and still remain good friends. There is no set amount you need to contact or see each other to remain very good friends. I have three very good friends from school, and a few more than I speak to from time to time. One of those was my best man, but actually I became much closer to him after school. But with all of them, I didn't speak much with them at all for the first year or two after we left school. We all made a bit more of an effort from about third year onwards (when we all turned 21, so we had birthdays to reunite for then), and maintained those friendships after that. But the actual amount that we see and speak to each other varies, and has varied over time. I've gone years without speaking to any of them regularly. But that is very much something that happens in life. Regardless, though, we have always tried to meet up properly once or twice a year, and this year for the first time we're actually going for a long weekend away together. We all have kids now, so that seemed like the best way to get some really sustained and quality time with each other. It's probably something we should have done sooner.
But around those friendships I've made other friends and drifted from other friends. Friendships will very much be in a state of flux throughout your life, and that's ok. Not speaking to someone for years doesn't mean you can't rekindle that contact, and you'll be surprised how often you can make new friends, even when other things in your life seem quite settled.