The previous responses have opposite viewpoints, so I thought I'd add my two cents as well so OP might be less torn. I'd side with
>>2 – just because you're now drifting apart, that doesn't mean that they weren't true friends from the beginning. Maybe they're not lifelong friends, but that doesn't make the time that you spent with them less important or the relationship you had with them less genuine.
But to answer your original question, I do believe friendships can last forever. They say that the average friendship lasts for 7 years, and after that, it's much more likely to have a lifelong friendship.
It does take an effort to meet up though, so again, I'd take
>>2's advice and try to keep in touch with them regularly. Maybe try to see if you can hang out with one or some of them individually too, instead of relying on a huge event where everyone has to come. My friend group can never seem to get all of us together when we plan something, but random handfuls of us meet up spontaneously for something really simple. Like a quick movie or something.