When a dungeonmans reaches level 10 you have the choice to retire by speaking to the Headmaster at your academy. Doing so will allow you to choose from three options becoming a professor at the academy, opening a tavern in the overworld or going your own way.
If you choose to teach at the acadamy, your current dungeonmens will create a new room at the academy where future dungeonmens can speak to the retired dungeonman to fully max out one skill tree which the retired dungeonmans had maxxed out. Which tree they will teach seems to be random but there are a couple requirments.
1.The chosen skill tree will not be one which there already is a proffesor for.
2.The skill tree has to be maxxed out.
3.This CAN include master degrees
Before choosing to open a tavern you need 30 purloined equipments. Once you have the required items you will get an item that allows you to open a tavern anywhere in the overworld. The tavern will have a shop consisting of all the items in the retired dungeonmans inventory. The stock doesn't seem to refill for each dungeonmans. However selling items to the shop seems to add to the stock for future dungeonmans.
Going your own way Edit
This is a third option for retirement. What it does is currently unknown.