I sometimes doubt these horrific figures; the casualty figures of the DRC war were recently reduced by half, so I think it will take time before we really know just how many people have really died in Ethiopia's civil war.
From what I've heard and gathered of different sources, the "estimated" figures stands somewhere between 600.000-1.200.000, if you include all types of fatalities from the war altogether. As there have been massive death of fighters, on all sides. From people I know who have crossed these "captured" roads (and seen countless corpses everywhere) and the footages online, it's in the hundreds of thousands.
This region was practically sealed off, from the outside world and barely anything was coming in and out. You can imagine the how people were suffering. So the figure of 600k of "indirect" war victims, isn't far fetched. Though, I do think it's broad to certain extent and include deaths of other causes too.
I think it is credible as well. I'm certain the figure is higher given how it ended. The Tigrayans accepted peace, there must not be many of them left. This was a genocide.
Jan Nyssen's assessment that so far there are between 150,000 and 200,000 starvation deaths, 50,000 to 100,000 victims of direct killings, and more than 150,000 additional deaths due to lack of health care.
The starvation deaths are based on the figures of the IPC Classification (400,000 people in famine, May/June 2021) and USAID (900,000 in famine, June 2021). The WFP did a study
https://www.wfp.org/news/severe-hunger-tightens-grip-northern-ethiopia
The number of deaths due to lack of health care is based on the excess mortality that it generates. In normal circumstances, an average of 6 people per 1000 inhabitants die in Ethiopia in a year, according to according to an instructive curve prepared by the World Bank.
https://data.worldbank.org/indicator/SP.DYN.CDRT.IN?locations=ET
During the conflict months of November 2020 to June 2021, they estimated that there were 20 deaths per 1000 people and starting with the total blockade 32 per 1000. Twenty out of 1000 was the rate of health-related deaths in 1984-85, before the improvements in the Ethiopian health system. This number has risen to 32 deaths per 1,000 since the blockade started. The excess mortality was then calculated, not on the entire population but on the total of 3.9 million people in need of medical care according to OCHA.
The tallied number of civilian direct casualties is at least 30,000. Probably they amount to 50,000 – 120,000, as there are hundreds of reports of civilian corpses “seen along the way when fleeing”, without mentioning location, date, numbers, etc.
Keep in mind the numbers calculated above are only until late 2021. 600k is probably an underestimate. This was genocide.