i personally dont think, the replacement thing should be limited, cause it could happen, exspecially with the few times, team size increased and the newbie-rule (no offense against my "newbie", Corrum is great!), and a 30-card-loss due to forfeit seems very hard. maybe 3 times and after that, you dont get salvation-cards, if you win, or anything like that, if we need such a penalty.
and, if a master cant fight, i think the substitute isnt allowed to use upgraded cards, cause at least a master should be able to stay in time-borders.
just my opinion