2000 Chevy Chevette Battery complete draindown

2000 Chevy Chevette V8

What is the situation when a car battery drains completely down? My experience is that it is very hard and sometimes impossible to get it to begin to take a charge again. Some say that the battery needs to be shocked to kick start it and remember which polarity it wants to be.
Some say that the battery is damaged when completely drained and the cells "die".
Is a relatively new battery that has been completely drained (left for a week or two with a drain until it appears to have no charge what-so-ever) worth trying to save or is it toast?
What's up here?

Thanks