Not sure on the dead question lol! I'd assume that they would be like most plants - if you scrape off a section of the trunk and it's green underneath, then it's alive.

But you can definitely rip off the new growth and plant it. Wait until they get to a size a bit bigger than your hand and then plant them where you want. It's that easy. I did it every year for five years, planted some, gave some away. Didn't even bother watering them in, just shoved them in the dirt. From two original yukkas, I ended up with 20 in my garden and gave enough away for four other gardens.