THEY die from beheadings (like any naruto character)
They die from chakra loss too I guess .
Yours Things to consider is false (Are you trying to pass them as facts)
Sakura healed that madara stab instantly . She didn't feel pain or suffer like other characters who were stabbed by him . That was how fast the healing was . Same goes to tsunade she healed her stab immediately after she took the Susano out of her chest .
You say "They are not instant " but Kishi said in his DB that they are instant and automatic .
The Byakugo is OP and many people agreed on that before but once Sakura activated hers everyone is trying to down play it. Smh.
Nope they would die. Only reason tsuande survived is because Karin, orochimaru, and suigetsu were there to help her.
Tsunade didn't survive that, Oro helped put her body back together. Madara took the life out of a Byagoku user if it wasn't for Oro, Karin, and Suigetsu helping her.
Oro and co helped speeding the process only . It was stated tsunade was able to do it but she "sacrificed" healing herself on the other kages .and even when she healed the kages ,katsuyu was healing tsunade however the process was very slow and here where oro help came . Suigetsu hold tsunade parts,Karin recover tsunade and katsuyu sticks her her body parts together .
P.S :tsunade Byakugo sozo saise was not activated . This all happend to the base tsunade . (Like I said she used Her Byakugo on the kages via remote healing)