I've experience that probably in the same ratio with IRL and Online contacts.

Sometimes people just go into different directions, it's sad but it's ok.

I've kept alive some online friendships from the bb forums, that I've met in real life a couple of times.

Similar to friends from HS, college or ex coworker friendships, sometimes interests change, they get into weird values you don't share or mature at a different speed than you. Sometimes it's just a logistics problem, it's hard to keep friends when you have a family, jobs and live in another time zone.

I've been ghosted by IRL friends as bad as with online friends. Outside of an awkward encounter in the mall or something like that, there is no real difference in that regard.