More about reincarnate: if you're a 200-year-old elf, you're still 200 after being reincarnated. But really the question is about the body. You get a new adult body—not young or old—appropriate for the body's race, so your inner and outer ages can be mismatched. #DnD https://t.co/nRj8JvVjdu
— Jeremy Crawford (@JeremyECrawford) November 28, 2017
Which age determines when you die of old age?
— Josh Watson 🧔🏻 (@josh_watson) November 28, 2017
If your soul and your body have different ages, bodily death is tied to your body's age, not your soul's. #DnD https://t.co/Q1XvJj3d95
— Jeremy Crawford (@JeremyECrawford) November 28, 2017
So that means reincarnate can be used repeatedly every time a creature dies of old to let them live indefinitely? That's correct.
— Jeremy Crawford (@JeremyECrawford) November 29, 2017
The existence of Reincarnate really makes you wonder why there are all these people running around trying to cheat death by becoming liches.
You want to live forever? Why risk the wrath of the gods, as well as risk going insane or being turned evil, just to become an eternally rotting corpse – a shadow of your former life? How is it better to live on as an unholy abomination than to just adopt a new body every few decades?
You don’t even have to do evil things to get the new body! No bathing in the blood of virgins, no stealing the youth and vitality of others, no nothing!
Yeah, okay – you need rare oils and unguents worth at least 1000 GP, and a Druid to work the magic for you, and it needs to happen within ten days of death (or however long you can be under the effects of Gentle Repose).
But surely that’s far easier to manage than all the work needed to become (and successfully remain) a lich?
Because there is no guarantee someone will always cast Reincarnated for you. You can’t cast spells while dead. Even if you create the conditions for the spell to be cast on you automatically upon death, there is still a chance you will die after being reincarnated before settings those conditions again. As a lich, you do it once and as long as your phylactery is not destroyed, you will be immortal.
There are also two more reasons.
A straightforward one would be the benefits of an undead body would outweigh those of a humanoid, at least for those ones who care about power more than the taste of food or other pleasures of the flesh.
A more intricate reason is the psychology and alignment of those who chase immortality. Those who would not be willing to perform the evil acts required to become a lich are less likely to want immortality. On the other hand, those who would not be deterred by those evil acts are more likely to opt for the more “permanent” and hassle-free immortality that lichdom offers.
What Sarezar said: You do the lich thing once and have it forever (pesky adventurers not withstanding). With reincarnation, you would need someone else’s help every generation. That’s a lot of people in the course of immortality.
And, it’s a druid spell. Druids revere nature. The cycle of life and death is an integral part of nature. Casting this spell to achieve immortality (or help someone else achieve it) would go very strongly against a core druid belief. So it will probably prove very difficult to get a druid’s assistance for this. The lich way may seem an easy path compared to that.