Reading C315/15, a bird strike is indeed extraordinary circumstances if the airline has further taken all efforts to avoid the impact of the delay. If the birdstrike happened on the 17th for SK943, then that flight plus the return flight would be covered by extraordinary circumstances. The 18th departure for SK943 would likely not be included.

For the other question, what is a covered amount, there are limitations for reasonable expenses, but I don't know where the limit is drawn.