It depends how you define "the economy" if you the think of only restaurant revenues (using the example), only then would it seem there is no impact to the rest

It depends how you define "the economy" if you the think of only restaurant revenues (using the example), only then would it seem there is no impact to the resturant economy. However, there are other measures of how we define the economy, eg. expenditure or income measurement derived GDP. Compare two economies one without flu (or depression) and one that has the flu. The economic output of the former would be higher than the latter, using those methods due to lost output or income. Waiters can cover for each other, what about those working full time? Ceteris paribus, a rise in depression that leads to the inability to work which will reduce the the size of the labour force and consequently output. Your last point on it being the "cost of genius" is pure conjecture. A rise in depression (tripling according to the article) has definite costs in terms of the economy (tangible) and human well-being (the intangible). It is in public interest to reduce the incidence of depression.