Various bits of lore mention that druids can, ususlly upon their deaths, merge with the spirit that inhabits their guarded lands.
In 2e, a 30th level psionicist/druid melds into their local spirit of the land, according to Earth, Air, Fire, and Water.
Rise and Fall has lower level druids merging with the spirit upon their deaths, existing in a kind of dream-like afterlife.
So, this begs the question…what do you think happens to these druids after merging?
For mine, I use three types of druid afterlives.
Wanderer Druids are those without Grove Master levels. When they die their spirits merge with the closest Spirit of the Land, adding their knowledge and memories to the existing Spirit of the Land. These slowly melt away over time as the base Spirit of the Land fully absorbs the power of the Wanderer Druid.
Guardian Druids are those with levels of Grove Master. When they die their spirits return to the guarded land and merge with a feature found there or an existing Spirit of the Land. A Grove Master who has not yet achieved 10 levels in the prestige class become a generic Spirit of the Land, slowly losing memories just as a Wanderer would. A Grove Master who has achieved 10 levels in the prestige class becomes a Spirit of the Land but retains memories, skills, and abilities. Until the Grove Master dies, she may leave the Guarded Lands for up to half a year. After a half year has passed, a Grove Master will die if she has not returned to her Guarded Lands.
Spirit Initiates are those who have taken the Spirit Initiate prestige class (Druid/Psions). They are on their way to becoming Spirits of Athas. They treat all lands as their Guarded Lands (irrespective of having Grove Master levels). When they die they form new Spirits of the Land where they have died. In the case of Grove Masters, they can choose to become new Spirits of the Land in their guarded lands instead. At 1st level of the Spirit Initiate class they are common Spirits of the Land, at 10th they retain all memories, skills, and powers just as a Grove Master would.