That's the harsh truth. You can be replaced easily. Maybe today you are a very important person for a company. It seems things will not run without you, but the company will appoint another person who will do the same job you are doing now.
Let's talk about the example you gave. An institution has a system. If you do a job, you can take leaves. You can take casual leave, annual leave, or even leave without pay. They may not give leave that long, but they cannot lay off someone like this. By the way, what happened to that brother? What did he do then?
RE: "If you dont persistent enough,you place will be replaced by others."