I took a guess that it was "half" the people I started with. By my memory, on launch day - the guild had 90-110 people online during prime time. (By comparison, Legion had somewhere in the high 200's.) By the time Vitality was trying to organize a raid for Nathria, we were down to 40-50 people online. I remember cause I was trying to help him and Alkorin was giving me the 3rd degree about getting banned for botting / selling combat routines way back in Legion. He wouldnt even let me get some stripped down version of an Officer to set calendar dates. Much less would he give it to Vitality for whatever reason. Fast forward a bit later and "someone" deletes the guild outright, which couldnt be restored by petitioning a GM. Wonder who that could have been.
I actually really enjoyed Nathria, Revendreth, etc. I wanted to level up through Maldraxus covenant on my Shaman here recently for the cosmetics, and I couldnt even make it through Bastion. Even after all the buffs and fixes Shadowlands received, sitting side by side with War Within - its just so obvious why SL's was a pile of shit for so many people.