Was Judas present at the introduction of Holy Communion?  We cannot tell by Scripture, so anything here is pure speculation. By the accounts of Mark, John or Matthew, there is no indication as to when Judas left. Luke could possibly have given us the indication, but we can’t really tell. Here are the arguments for and against:

Reasons for thinking so: Because of Luke 22:20-22. Jesus is saying that the person about to betray Him has his hand on the table (meaning “now, at this time”). However, we do not know if Luke condensed the evening’s conversation, and wasn’t concerning himself about a timeline of events. We would have to study the book of Luke to see if Luke has the habit of discarding timeline, in comparison to Matthew, Mark and John. Even then, we can never say for sure if Luke disregarded the timeline for the Last Supper or not.

Reasons for thinking not: Jesus is clearly instituting a remembrance of Himself, of His sacrifice at the cross and the meaning of that sacrifice. Judas has no part in that, just like other non-believers. I do think that Judas was present at the foot washing because of John’s account; John 13:11 was said during the foot washing part. How come no one questioned Jesus as to who “wasn’t clean”? Perhaps they did and it just isn’t recorded. This point is important to remember when reading the Bible: not every event is recorded, and out of the events recorded, not every action or every word is recorded. John, at the end of his account of Jesus’s ministry tells us that clearly. See John 21:25 for that message.