Among the many urban legends governing the software industry, the one which has gained currency in recent times is the one about no engineer being irreplaceable. We've all seen it in action - many times, a lead developer quits in the midst of a project, and yet the project reaches fruitition. A manager may leave, but the project gets completed on time, on budget. In fact, a rather gory saying for this phenomenon, where you can simply replace an engineer by an other, is: "If your lead engineer gets hit by a truck, your project should still run on schedule."
However, is it true? Are engineers replaceable/dispensable?
I don't know. Years ago, the team lead, my mentor and guru for my first project suddenly quit. He was followed by two other senior members in the team. Now, all we had was a team of freshers, and the average experience of the team in that domain was around 6 months (down from around 2 years). Still, we pulled the project through. A couple of years later, two of my close friends left the team. The project went on as usual. Then, I quit, and there was still no material difference to the project - yes, people worked harder to make up for the loss of a teammate, but otherwise, to the external world, everything was hunky-dory. Since then, I've left two companies, and many people have left my place of work, and life went on as usual.
What this ignores though is the sociological aspect. In a well-jelled team, every team member has a place of his own - not just technologically or organizationally, but also sociologically. Invisible threads of trust, of emotional support, of friendship that take months to build are usually torn off when a person leaves. Those are harder to replace. When the seniors in my first project quit, the rest of us were able to take over the technical and organizational aspects quite well. The ten things that my mentor was responsible for, we split amongst the four (or five) of us. What we couldn't split (immediately) is the sense of confidence of having someone to turn to when we were in trouble. What we couldn't take over was the friendly smile that greeted us when we approached him with a problem. Ofcourse, with time, we built support structures of our own - which were again dismantled when people left.
I think this is the aspect of turnover that is largely ignored by companies. What thinks you? Use the comments link freely to express your opinions.