When most mobs are name-tagged, such as a zombie, that mob will never despawn unless killed. However, there are a few exceptions like the wandering scammer, and this mob, the vex. Vexes naturally die within 30 to 120 seconds of being summoned by an evoker, regardless of whether they are name-tagged or not.

Steps to reprodue:

1. Spawn an evoker
2. Spawn a villager to make it spawn vexes
3. Rename the vexes using a name tag
4. Wait

Observed result:
The vexes still take damage.

Expected result:
The vexes should not take damage, since they are renamed.