Complex sentence: Micky joined John Mayall's Bluesbreakers for a few gigs in April 1967, while while Mayall looked for a permanent drummer, and was soon replaced by Mick Fleetwood-who had also played with Steampacket.
Split into simpler sentences: Micky joined John Mayall's Bluesbreakers for a few gigs in April 1967. Micky only took the place while Mayall looked for a permanent drummer, and was soon replaced by Mick Fleetwood-who had also played with Steampacket.