At the second level of the Ondra's Gift Lighthouse, I had my druid summon a Small Wind Blight ... to distract some of the Shades and Spectres in the distance.

 

The Blight survived the entire battle. Full endurance and health.

 

Afterwards, I moved upstairs ... explored there ... moved downstairs again ... outside ... to the Heritage Hill guard post, tried to have the Blight talk to the guard *lol* ... then onwards to the city map ... to Brackenbury district. Still accompanied by the Blight. There I was ambushed by assassins, who managed to kill the blight with crossbow fire.

 

It's the first time for me a small blight has been with the party for so long.

 

What is the typical summoning duration of blights?

 

It is an intermittent bug. I had it happen to me once before on a Beetle summon (via figurine). I had to force attack the summon with my party to kill it.