Way I see it, look at Ukko's and Smite. Everyone panicked when SE announced the nerf, but it wasn't as bad as people thought it would be (only a nerf to their native critical hit rate iirc)

Now if we look at Perfect Defense and what they could do with it. At the moment it starts off with around -90~95% Damage Taken and Resistance to most stats, decaying after 45 seconds or half duration. If they reduced potency to start at say, -75% Damage Taken, it would still be fairly decent, and not completely overpowered for the 30 minute recast on Astral Flow. You would require more healing power, but either way, thats likely to be needed anyway. imo, nerfing the duration would have a much worse effect on it.

Embrava on the other hand is a much different situation. Embrava excels at capping magic haste (when used with Haste itself), and providing a strong Regen and Regain effect. At the moment, a capped Embrava will provide 34% Haste. If they reduce the Haste on Embrava by any more than 5%, you no longer cap Magic Haste. The regain I don't see getting nerfed too much (maybe one/tick), making a 30min-1hr specific spell the same potency in Regain as a XI Tactician's Roll would be extremely unfair despite Embrava's other effects, and then possibly prompt a nerf to Tact Roll. Nerfing the duration would put a serious hindrance on Neo Nyzul, but I think this is the most likely route they'll take unfortunately.

On the other hand, now's the time to ask- for the love of god, give the current Astral Flow Blood Pacts (barring Zantetsuken) a damage boost.