This is a great ideal to aim for: that at any time you can be asked to step away from your code and, not only does it continue to function superbly, but those who carry it forward want to reach out and hug you for the fabulous work you've done.
If your code needs you around to run correctly then you're certainly not doing things right.
How can you ensure that you can walk out the door and not have the world come crashing down?
* Simple, intuitive interfaces at every junction
* Write great documentation
* Refactor and integrate until you can sleep well at night
* Study the documentation of the APIs you utilise like a hawk
* Study other people's code for good ideas
* Do meaningful code reviews (not code exhibitions)
* Log dogmatically
* Eat your own dog food
* Run on the mainline branch
* Be willing to break your neck trying new things