It is common situation, you know?
Most of language exchange friends are like this, but some people sre so nice.
I talk to my friends about anything in English like Japanese friends. Tbis is the most good thing to learn English.
'Disappear' sounds like suddenly not responding anymore at all. That's just rude, they shouldn't do that.
But discontinuing the language exchange (with some notice) can happen. It could be you're not a good match, but it's also common for things to come up in life. Some things are more important than learning languages.