Is it possible that the Illusionary World or the field that Tomoya apologizes to Ushio in could be considered Mag Mell?

Neither the Illusionary World or the field of sunflowers would be considered as Mag Mell. To prove my point, Wikipedia says it's "a place where sickness and death do not exist". Having said that, Ushio of the Illusionary World "died". Meanwhile, the field of sunflowers is located on the real world, a world to which we all know, death and sickness exists.