Quartz
Hero
Can I harvest the "piece" in advance (say, a tooth) while I'm still alive, and then cast Reincarnate on the tooth?
Sure. A lock of hair might be easier, though.
Additional question. Disintegrate mentions "the creature can be restored to life only by means of a True Resurrection or a Wish spell". Does it mean Reincarnate won't work?
5E is exception based so Reincarnate won't work. But Rule 0 applies. If you want it to work, it works. But maybe there are complications overcoming such powerful magic...