Glad your mollies continue apace. Disappearing swordtails aren't uncommon. She could have jumped and worked her way across the room. (Ah... and do you have a cat or dog.?)

Or, since your aquarium is probably well cycled now and very active biologically now, both cannibalism and just active bacterial action could dispose of the body fairly quickly. Possibly both were involved.

Swordtails, like so many live bearers and killies, are somewhat cylindrical in shape. That is the design of a fishy sprinter. When startled they will explode for 3 or more feet - in the water or out of it. That kind of instant, almost reflexive jumping, works fairly well in nature to avoid predators (be they fish, birds, reptiles or even mammals) at first shadow. That doesn't always work out so well in aquaria. :)

Sometimes moving an aquarium stand or bookcase, after a few years, which has held an aquarium or two can be startling. One may find a surprising number of crispy critters. :(