>>96667482
>IIRC they could retire but had to drop down in level
Losing a level happened when two druids had to fight for a position in the hierarchy and the challenger won. The challenger would lose all their XP to gain that level if they lost.
The "retirement" you're thinking of is druids becoming hierophants, where they basically forfeited all responsibilities in the order, all their XP, and became immortal elemental planeswalkers by level 20. The XP requirement for gaining your first level as a hierophant is greatly reduced, but 500,000 is still nothing to sniff at.