Discord certainly has some advantages, such as being properly supported in modern browsers and smart phones.
That said, I was under the impression that part of the draw of the chat was its ephemeral nature - that what's said in chat stays in chat, because there's no record of it otherwise. Discord, however, does keep a log of written messages, so that you can catch up on discussions you missed while you were away. What's written will remain, at least until someone explicitly edits or deletes it.
I'm not saying Discord is a bad idea - I quite like it myself - but it's not exactly a drop-in replacement for how some folks were using the flash chat.