Complex sentence: Osbourne briefly left the band following the tour in support of the album and, although he would eventually return for the follow-up album "Never Say Die!", the band temporarily replaced him with former Fleetwood Mac vocalist Dave Walker.
Split into simpler sentences: Osbourne briefly left the band following the tour in support of the album. Though he would eventually return for the follow-up album, "Never Say Die!", the band temporarily replaced him with former Fleetwood Mac vocalist Dave Walker.