There are various answers: a) There should be no key developers, no indispensable people in your projects. This is often hard to achieve on small companies. b

There are various answers: a) There should be no key developers, no indispensable people in your projects. This is often hard to achieve on small companies. b) Communication: In a group of developers there should be good communication about ideas and functionality. Documentation helps a lot, but sometimes just sharing the basic reasoning behind a component is enough to carry on. c) Adaptation: Provided there is a lack of a) and b), your team should be good enough to adapt and survive to such drawbacks. Now, for your particular case (I believe you are in c)), consider what will be better for the company overall? What will take you less time or be better in the long term? Trying to understand the current code or writing it from scratch? I wouldn't worry about what will happen when you leave the company in two years time, because whatever path you choose, you should follow a) and b) to prevent from this happening ever again. Write documentation, share your ideas with fellow developers or even team up with some for this project, don't take on it on your own. Hope this helps.