Guilds disband in all tiers, sure, but I got a feeling that in ToS numbers of guild who disband is already really high, and its only been ~2 months since release. I don't have any exact statistics, just my feeling. Also as a GM it was never harder to recruit people than now, is it because my realm is dead pve-wise(sylvanas) or people just cant be bothered raiding i dunno, but my guild is on the verge of disbanding too due to people quitting mythic raiding and going casual.