Key legal question
Was the substitution from the seller to C. AG procedurally admissible without the appellants' consent?
Extracted holding
Yes. Where active standing passes during pending proceedings, the successor may enter the case without the opposing party's consent; the challenged cantonal rule was not unconstitutional.
Extracted reasoning
The Court distinguished a purely voluntary party substitution from substitution following a transfer of the substantive right. In the latter situation, the defendant is not prejudiced in the same way, because the original plaintiff was properly entitled when the case began.