Sadly that isn't how it works. There are "different" Sages all going on at the same time. So if 5 people in *X Group decide to not enter, then it will just put players from another sage group into the one they were supposed to be in.

Also, if you sign up and leave purely to get credit for attending - you must participate in at least one fight. I join, attack someone, then refresh.

There is literally no point in doing sage as a f2p. None.