Conversation so far:
who did the lineup instability with wishbone ash start with?
Turner was replaced by bassist and vocalist John Wetton.
where was John Wetton from?
John Wetton, formerly of Family, King Crimson, Roxy Music, Uriah Heep and UK.
did they release any songs sung by John?
featured Wetton's lead vocals on just one song.
was the song on an album or was it a solo song?
Number the Brave was released in April 1981 and featured Wetton's lead vocals on just one song.
how did he react to the just one song idea?
Wetton did not continue with Wishbone Ash beyond the album sessions and rejoined Asia.

Question: who replaced him?
Self-contained rewrite: who replaced Wetton in Weishbone Ash?