(a) A plan of merger shall be consented to by all the members of a constituent company. (b) Subject to any contractual rights, after a merger is approved, and at any time before articles of merger are delivered to the Mayor for filing under § 29-809.04, a constituent company may amend the plan or abandon the merger: (1) As provided in the plan; or (2) Except as otherwise prohibited in the plan, with the same consent as was required to approve the plan.