The issue I have with bringing a loser back due to a forfeit is, it should be the next best "Overall" qualifier. This makes it fair to everyone. It will also make every rack in the preliminary rounds important, even in a blow-out because more than likely it will come down to "rack differential" to determine who gets to advance.
Rald should be forfeited and Ko awarded walkover and get to play in final
But for sake of argument if they have to replace Ralf, best overall qualifier is better criteria then just next best qualifier from group. If it is best overall qualifier then we look at 2nd place finisher in each group and since they all have 2 wins 1 loss, the tiebreaker is rack differential
Appleton +3
Shane +3
Dechaine +2
Chang 0
So it will be choice between Appleton and Shane as replacement