h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Frank Zappa was in fact pushed from the stage into the orchestra pit resulting in serious fractures, head trauma and injuries to his back, leg, and neck, as well as a crushed larynx (which caused his voice to drop a third after healing). This left him wheelchair bound for a time, forcing him off the road for over a year. (He was wearing a leg brace for a period thereafter, had a noticeable limp and couldn't stand for very long while on stage.) He said one leg healed "shorter than the other" (a reference found in the lyrics of "Zomby Woof" and "Dancin' Fool"). Meanwhile, the Mothers were left in limbo, and eventually formed the core of Flo and Eddie's band as they set out on their own.
The end of the working relationship between Mark, Howard and FZ was largely because of this incident. However, it would appear that relationships between Flo & Eddie and Zappa remained friendly - they were the supporting act for Zappa at The Cobo Hall in Detroit in 1976 - and guested with Zappa for example.
Howard and Mark auditoned again for the Zappa band in 1987 and negotiations got as far as some rehearsal sessions as captured on the bootleg 'Europe, Backstage & the Mystery Side'. Rumour has it that it was Flo & Eddie (and not Zappa) who decided not to pursue this opportunity. Either way they did not form part of the legendary and last Zappa band that toured in 1988 throughout North America and Europe before self-destructing.