Silica no longer 1-shots the boss due to a bug so everyone is going to have a fair attempt at the same event this time around. It's going to be rough for anyone who is attempting this for the first time.
SAO Memory Defrag – Shadowflash Slash EX/Master Missions
Aside from the usual free MD for completion you can also earn some dark medallions if you satisfy specific clear requirements. Here's a quick guide on how to tackle the encounter.