No one is indispensable, the sooner we realise this the better .No one is indispensable in this World and everything and everyone is replaceable. We need to live with this realisations all the time or we may end up having bitter experiences.
Even this feeling that I am indispensable causes ego and arrogance take over one's sensibility and humbleness and in turn takes him/her down the hill.
I would share an incident of my senior or say my reporting boss who was head finance and was in the organisation much earlier than me. He had experience and skill but slowly he became arrogant and egoistic. He would say that this is his last job and he would retire from this organisation, as he has given his blood and sweat to build this organisation. He was very confident and sure that there is no one who can replace him, ever. His behaviour slowly turned arrogant and steadily that led to his downfall.
Recently, I came to know that he has resigned from his post or in short he was asked to resign for sake of leaving with dignity. Since, I have already resigned 2 years back, so I couldn't find out the exact reason. But, I remember his words very well as he used to repeat that no one take his position many times.
What I observed that, having knowledge and skill is one thing but having humility and good attitude towards others also matter a lot. We are not indispensable and sooner or later we will get replaced, it is just a matter of time. Living with this clarity is very important to save oneself from jolts that life may throw upon us.