Villagers don't change professions when they naturally generate in a village

Steps to reproduce:

1. Go to a village that has villagers
2. Go to the workstation of a particular villager (Like a farmer)
3. Break the workstation

Expected result:

Villager should lose its profession

Observed result: 

The villager still keeps his profession

Therefore, the villager will keep his profession regardless if you traded with him or not.