Well... Those things are kinda both partially true. Whilst 9,700 Custodians are now out doing Crusading and helping Rowboat in the name of the Emperor, 300 are still back in the Palace as the chosen Companions of the Emperor. These were the Custodians shown to be sans armour in previous works, though other new lore mentions that the Custodes armour eventually goes black from the seering radiance of being close to the Emperor for so long. The longest a Custodes has ever served as a Companion before needing to be switched out is 100 years.<br/><br/>As for the daemon incursion at the Webway Gate, that's totally a thing. It lasted for five years after Magnus busted his way through to warn the Emps of the Horus Heresy before Big-E managed to seal it up (005-010 M31). Malcador had to get on the Throne when Emps went to the Vengeful Spirit to fight Horus in order to keep the Gate sealed. You know the rest. Basically if anything were to happen to Big-E, the Gate may unseal and Chaos could overrun Terra.