One thing I’m going to predict going forward is that Avatar 4 & 5 will 100% happen given the commercial success of this movie and also the fact that a lot of the reasons TWOW's budget was so high was due to advancements in technology.
But most of all, it will happen because Disney does not own Avatar. They own the distribution rights, yes. However, James Cameron owns Avatar just like he would own Terminator had he owned Lightstorm and had as big of a name for himself back in the early 80's as he did when he pitched Avatar to Fox. James Cameron owns most of his catalog, including being the sole production company on T2 and one of two production companies on Avatar 2. The second is not 20th Century, meaning that Disney will potentially need to pay Cameron in order for it to stream on Disney+ since they don't own the film in any way.
Them not owning the IP is why 4 & 5 will get green lit by Disney. If Disney doesn't green light them, someone else will and Disney isn't going to want to let the franchise go as they would be at risk of losing the entire franchise from their arsenal. It's kind of like when they bought LucasFilm, but that only got them so far as it didn't get them ownership of the original trilogy or the prequel trilogy until they bought out Fox. I wonder if Disney will try and purchase Lightstorm from Cameron eventually, although I doubt he would sell.