Who says its official? There is no direct statement about Johnny leaving the series. Its only Stuart Beattie's interpretation based on where thing currently stand. As the article itself points out, Stuart Beattie has NO direct involvement with what is going on, so therefore any words from him contain NO official confirmation towards anything at all.
More to the point, given the phenomenal success of movies like Halloween (2018), a movie which made more $ in its opening week than ANY of its series' previous instillments did in their entire lifetime gross (and even more than at least 3 of them combined), and it happened to feature thee two original lead actors reprising their iconic roles, along with returning to the same tactics, methods and elements of the original.
If Disney is truly being their true smart selves, they will know that they can't just fully reboot and completely write off/recast an actor with who a character has become so close associated with, hence one of the main reasons why Solo bombed so heavily for them, not to mention for Sony the Amazing Spider-Man movies, of which Disney had to make an unprecedented deal with in order to salvage for them.
In short, if it is a complete reboot/re cast/write off, NO ONE, NOT even Disney themselves, will EVER end up being truly happy with it. It WILL overall fail, NO MATTER how it may initially seem.