After a couple of hours fuel burn and 2.5 passengers (in weight terms) I would have thought even a Seneca could maintain height on one engine at that altitude unless it was iced-up;
Really.
According to the report posted the accident site was at nearly 6,500 feet.
Are you suggesting the pilot would have readly been able to maintain height on one engine given the single engine service ceiling and the need to maintain some rate of climb at times even to maintain the existing altitude?