Interesting, I never thought about this.
Now that you mentioned it, I read more about
Horcruxes.
There are several methods to destroy them.
The poison blood (Blood manipulation technique?)
Gryffindor's sword (Maki's sword?)
Fiendfyre (amaterasu?)
Killing curse (Dont know who can use it in JJK)
Remorse (Like Sukuna will ever have any remorse lol)
It is said that the person becomes more evil if he keep on creating more Horcruxes. Their body also changes shape, like we saw Mummy Sukuna in raws.
Horcruxes are soul fragments and they exist in host's body in a limbo (we already have this confirmation; Yuji x Sukuna interaction).
And when the host is damaged beyond repair, it damages the Horcruxes soul fragment.
At that time, the host has the option to continue living as there were two souls in his body, so he can let Horcruxes/soul fragment die.
This is how Harry Potter survived.
The implications of this are insane!
Kenjaku waited for Mahito to perfect his Idle Transfiguration. All about souls!
He created Choso with blood manipulation.
He had Yuji, a human body that Sukuna cant take over.
(Or maybe I just want Kenjaku to betray and backstab Sukuna 💀).
Edit; I think Sukuna is intentionally not consuming his other 5 fingers as insurance. Like Voldemort, he hates death. So, he will do anything to continue living forever.