If your employer doesn't hire enough bodies to make sure the work gets done when people call in sick or take PTO, that's on them. Absenteeism can range between 3-5% on any given day, and can be industry dependent. This is something that should be factored into the amount of work that needs to get done per day on average when deciding on appropriate headcount. Companies that want to run skeleton crews because, "muh profits," can find out when they fuck around. I was always taught that when it comes to things critical for your survival, you should always have them in triplicate. This is why I have an E-bike, analog bike, and bus pass; if one stops working, I have backups. Employers should have this mindset with critical tasks and headcount.