I like to tell people that the end of the lengthening phase is when LL begins, not when it ends. When I first left the hospital, I could barely balance myself enough to use a walker. I had to lean way forward and put my whole body weight on the walker in order to avoid falling backwards. It took me two hours to walk around the block, which is normally a 10-15 minute journey. I spent about two months needing the walker to get around before I was able to graduate to crutches.
I spent another two months needing crutches to get around. At about the four month mark, I was finally able to ditch the crutches, but my walking was still really, really slow. Stairs (especially going down) continued to give me a really hard time. It was easier to walk backwards down stairs than forwards.
It was about 6-8 months after leaving the hospital before I had regained enough strength and flexibility to walk somewhat normally.
I've never heard of someone having their leg snap after the rods were removed until it happened to programdude. Either his bone wasn't consolidated enough when the nails were removed, or his muscles just created too much tension for the bone to handle. The former seems more likely, but I'm hesitant to think that a doctor of Rozbruch's caliber would make such a mistake. So it remains a mystery.
To answer your final question, I think 3 years after lengthening or 2 years after nail removal is a good rule of thumb for being truly finished with LL. Your results, of course, may vary.