Well, This one relies on the Guide the the Crystal Gems book, but only a little.
|Unhealthy Fusion Theory|
|Title||Unhealthy Fusion Theory|
|Date of Publication||10/14/2015|
Listen to me! You've been fused for too long! You're losing yourselves!
|—Pearl, "Coach Steven"|
This is what happened to Malachite off-screen, except she's been fused way longer. Now, here's something many people noticed in the Guide to the Crystal Gems book. There's a character page for every gem and fusion in the show so far. Malachite's entry is by far the most interesting for one reason:
I'm not Lapis anymore...we're Malachite now...
|—Lapis Lazuli, "Chille Tid"|
Every other fusion page lists all the locations for every gem in the fusion. Malachite's page only lists the nose. There's obviously no space constraints, and while it could have been a typo, it would be unusual to omit an important fact like that. If this was deliberate, then we can only assume that Malachite is now her own gem, and that Lapis and Jasper are gone for good. So, what have we learned? Unhealthy, Unstable fusions can cause the component gems to literally lose themselves and become one.