Instead of Lichdom (Lichery?) being the end result of a lot of effort, why not make it the inevitable result of a lifetime of meddling with chaos? At some randomly determined age, a mage starts to slowly dry up and desiccate. Remember that in ancient times, 40 was considered quite old to many, so perhaps 30+2d20 would be an appropriate age for the transition. Over the course of the year, even if no adventuring or spellcasting happens, the mage gains a level and no longer resembles a living human.
The lich-in-transition would suddenly take an interest in cosmetic illusionist spells, anti-stench spells and start looking for a safe base of operations and perhaps servants. At any rate, he or she is suddenly unable to knowingly commit suicide or allow someone to kill them without a fight.
When I do get a campaign going next summer, I’ll use a lot of the ideas from my series on the Magic User. One of the more important ideas in it is that Magic Users are not trusted or wanted at all in society. They are the ultimate taboo to normal men. Perhaps part of that is that they have the reputation for becoming immortal ghosts or demons. Among the magic using community, there may be a profession of slayers, whose job it is to kill those who begin to turn.
Here’s your plot hook: There’s a mage caravan headed out toward Vulture Pass, hoping to make it south for the winter. They are lead by Marius, a tenth level mage who must be at least 50 years old. There was a rumor that Marius had a bad smell about him at the last Gathering of the Argnac clans. One of his students and a mercenary were sent by the Great Bulwark to investigate last spring, but there has been no word sent back.
The party is somehow asked to look into it. Perhaps the party mage is a former apprentice of his, or a niece. Some possible developments (Roll 1d6) :
1- Marius is a lich and has killed then animated is caravan.
2- The investigators were killed in route by bandits, Marius does indeed smell but is not a lich.
3- Marius is actually a mage/vampire. He has converted the two investigators.
4- Marius is in the process of turning, has unwillingly murdered his caravan and others to protect himself and will desperately fight the party he hopes will kill him where others have failed.
5- Marius is not a lich, because he has found the fountain of youth.
6- I can’t think of 6 tonight. Roll again.