Complex sentence: Rock promoter Bill Graham wrote a letter to Warner Bros. to convince them that the real Fleetwood Mac were in fact Fleetwood, Welch and the McVies, but while this did not end the legal battle, the band was able to record as Fleetwood Mac again.
Split into simpler sentences: Rock promoter Bill Graham wrote a letter to Warner Bros. to convince them that the real Fleetwood Mac were, in fact, Fleetwood, Welch and the McVies. But while this did not end the legal battle, the band was able to record as Fleetwood Mac again.