I still have one online friend from 2005, we'd met on a forum for a group that has since disbanded, but yeah we still follow each other on Instagram. We don't talk a lot, but she reacts to a lot of my posts and I hers.
On the contrary, I met this girl Caitlyn on the One Direction forums in like... I want to say 2013, and we became so close that we exchanged Google Hangouts and Twitter info and would chat very often outside of the forums. But then one day, she confessed that she stopped liking 1D and was ditching them for 5SOS. I wouldn't have minded bc I was a 5SOS fan back then, too, but after that, she quit the forums, deleted her Twitter, and just fell off the face of the earth. So that frienship lasted maybe a year.
So yeah, it can depend from friendship to friendship. Maybe this one will last more than 2-3 years, who knows?