Blazes do not despawn even when following despawning requirements listed on Wiki. 

Light level is above 7 (I’ve surrounded them with lava and lit the area with red stone lamps. 

Player is 5at least 54 blocks away.  I’ve spent a few hours moving into and out of this range, making sure to keep the chunk in which the blaze naturally spawned loaded at all times.  

After many hours of observing them, the blaze will not despawn the way all other mobs have in the same area. 

Playing on Windows 10 and latest iOS on iPhone 8 Plus on Realms.