Redundant skills (That don't stack)

In the Arena, I came across an Ayra with Ayra's blade, and Heavy Blade A-skill.

Considering (Ayra's Blade + Heavy Blade 3)
and (Blazing Durandal + Flashing Blade 3)

They arent supposed to stack but...
If one blade fails can the other blade still work?
And is that a good strategy?