I've done this many times, I know for a fact that almost NONE of the prep work, training, file organization, email handoffs, exit/handoff plans, and so on...were ever used except to allow somebody to make excuses on their 'delays' in the first few months after I left. I've also worked in industries for many years, and was told this line about 'leaving on good terms'. Honestly though, you could just about nearly commi…
Outside of very specific circumstances, it's probably not the least bit true. Most of us simply aren't that important, and very few of us are that important that a team will be screwed if we GTFO ASAP. I can count on more than one hand the times that the lead developer or PM were gone for multiple weeks and virtually nothing changed as a result. If coworkers are indeed screwed by your departing without taking a month to do prep work, that's more often a sign that the company is dysfunctional. It's a rare circumstance that someone has unique skills and knowledge that aren't easily replaced.
I've had my share of times where I left a company either less than two weeks after or immediately upon quitting, and have never been shunned by coworkers I was on good terms with. It just doesn't happen. Nobody cares. If anything, I've been praised by coworkers I've been reaquainted with at other companies for leaving behind a dysfunctional environment with few f@$#s given.