Firing someone after they notify you of an inability to be present is bad, and there are many cases where it’s illegal, such as in the U.S. when FMLA paperwork exists. We’re not discussing that, nor are we discussing how a real manager reassigns mission critical work and doesn’t blog about hirings and firings. No—we’re discussing whether it’s hypocritical. I disagree with your usage of the word “most”. I truly do not believe that most workplaces are one person away from missing an important deadline. Most workplaces I’ve experienced get over it extremely quickly, but that is just as anecdotal as your workplace experience.
If we assume most workplaces are exactly like your hypothetical workplace, which is to say, happy to let someone go despite how long hiring someone new will take, then these workplaces are still usually not up against the wall when it comes to someone taking time off; they instead spend most time in a state of not caring whether or not they have full staffing, which means taking time off shouldn’t be an issue for most of the year. So again, in a world where every workplace is understaffed and hyper focused on deadlines, the mathematical odds are that this action was still hypocritical.
But those are just odds! I could be wrong. This person who publicly posts about workplace drama and fronting may also also be a very fair and judicious person. Maybe they just care so much about their clients.