Saying LB was the heart of Fleetwood Mac is lan interesting take on things! Not one shared with the vast majority.
You don't consider Paul McCartney a lead singer or core member?
Seriously, how can you say that? If Mccartney can tour from 1989 to 2018 dong 50% Beatles material, without core elements of the band - Lennon, Harrison and Starr...then certainly Fleetwood Mac can do it without LB.
If the band are up for it , it's their choice and right.