A staff member is likely to come by, so to save time, I'll post the formulation of the Durability changes that were discussed.
In Hero mode:
Varies from Large Mountain level to Large Country level for getting KO'ed (Varies depending on how much she focuses on defense), Universe level for getting killed (As the Fairies are parts of Shinju, who is a Universe level God, they grant Heroes protection from everything and anything of that level)
In Mankai mode:
Varies from Large Mountain level to Moon level for getting knocked out of Mankai (Varies depending on how much she focuses on defense), Universe level for getting killed
At the end, I'll add a note: "Over the course of the series, the Heroes have battled Vertexes of varying levels, ranging from Large Mountain to Moon level. When focusing on defense, it has been shown that Heroes can tank anything up to Large Country level (Scorpio Vertex) in Hero mode, and up to Moon level (Leo Vertex) in Mankai mode. However, on several occasions, whether in Hero or Mankai mode, Heroes have been knocked out by surprise attacks against which they didn't react in time. The Heroes are however unkillable by anything below Universe level, due to the divine protection they receive from Shinju, their God, via the Fairies."