This is pretty much a typical factor to consider with online friendships. Although it's also the same with real life friendships or ones you make in person as well. Suddenly they decide to stop replying to you texts/calls, and just like that... they have disappeared from your life. Unlikely to be seen again. Even if you do maybe a long time later, they will have completely no recollection of you.
Enjoy any good things, even the little and menial ones, as you will never know what impending distresses could descend upon you in a moment.