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Good bye yin seal
First, you are assuming Sakura will get hit by Hinata, and since she is smarter, faster and with more stamina than her, has a one hit KO and ways to prevent Hinata from approaching, I find that extremely debatable.
Secondly, you are also assuming Sakura will need to open the seal to defeat Hinata, given her superior skills, I also find that very unlikely...
If she doesn't open the seal, the stored chakra is perfectly safe from Gentle Fist, and if she get to Tank some punches, she could always release the chakra and unblock every coil affected and regenerate every internal wound.
In third place, even if she gets hit by Hinata while Byakugou is active, this S class regenerative technique that works on a cellular level wiill recover every injury, internal or external, instantly. It's not medical ninjutsu, It's regeneration!
"The absolute pinnacle of medical ninjutsu, created by the greatest of medical ninja, Tsunade, it is the ultimate regeneration technique.
By releasing the great volume of chakra stored in her forehead at once, the body's cell division is forcibly stimulated by proteins, reconstructing all organs and all tissues making up the human body. The technique itself does not regenerate the old cells, rather it hastens the creation of new ones through division. If this technique is used, a body whose vital organs are so gravely injured that it cannot bear it any longer will be instantly restored to its uninjured state. By Tsunade's own claim, as long as she has chakra it is impossible for her to die by any means, as such she gains a form of "immortality" throughout the duration of the technique."
There is no way Byakugou can't heal that.
Yin Seal and Cursed seal are both sealed sources of chakra , and that scan shows that Neji was able to prevent Kido.aru from accessing his cursed seal after hitting him with a jyuuken strike.
No, Neji just dissrupted the chakra on his flow, making Kidomaru unable to use chakra from his network... His seal was already open.