Here is the relevant clause in the Contract of Carriage. Note that it references fare class paid and you could argue that...maybe. The real killer is :
a) Transport the passenger without stopover on its next flight in the class of service
comparable to the fare paid as the passengers original outbound flight or on a flight/s in
a lower class of service, acceptable to the passenger, on which space is available at no
additional cost to the passenger, or

The fact that the flight was taken would be proof of acceptance no?


C) INVOLUNTARY REVISED ROUTINGS
1) Schedule Irregularity
NOTE: Schedule Irregularity does not include force majeure events as defined in paragraph (D)
of this rule.
When a passenger is delayed at time of departure due to a schedule irregularity occurring within
24 hours of the original scheduled departure time, DL will:
a) Transport the passenger without stopover on its next flight in the class of service
comparable to the fare paid as the passengers original outbound flight or on a flight/s in
a lower class of service, acceptable to the passenger, on which space is available at no
additional cost to the passenger, or
b) Endorse to another carrier or to any other transportation service the unused portion of
the ticket for purposes of rerouting, or
c) Reroute the passenger to destination named on the ticket or applicable portion thereof
by its own services or by other means of transportation; and, if the fare, excess baggage
charges and any applicable service charge for the revised routing is higher than the
refund value of the ticket or applicable portions as determined from Rule 90
(REFUNDS), carrier will require no additional payment from the passenger, but will
refund the difference if the fare and charges for the revised routing are lower.
Exception 1: Passengers holding other than First Class tickets will not be involuntarily
rerouted on First Class services of other carriers without additional
collection.
Exception 2: Passengers will not be involuntarily rerouted on Concorde aircraft