He freaked out cause hk dying directly affects him
He can't be immortal because he has their souls. Cause they are also basically immortal. And it's implied/basically confirmed to be because of imu's power and the contract.
So it would be an ouroboros situation.
It makes more sense for imu to give part of his own soul/power to hk.
I still think this is the real reason for all the slavery.
Imu needs souls to feed off of, and uses the Heavenly Tribute to:
A: Find slaves to be sacrifices, and
B: Use psychological tactics to destroy their Will so he can consume them
This also 1000% explains why people like Kuma TERRIFY Imu: the fact that he can't just break them the way he can most people, the fact that no matter how much he tries to hurt Kuma, Kuma acts kinder/better as a result, just fucks up Imu's entire system.
This is unironically why Koby is so dangerous to Akainu's rampant militarist bullshit, too, while being an even bigger threat to Imu: he's proving the "you need to be a hardass, unempathetic, STRONG SOLDIER" to be powerful is complete fucking bullshit.
You can be strong as fuck like Kuma/Shanks and still be a kind Soul.
Another big reason I believe this theory is it would mimic Big Mom taking Souls from her people (but doing so consensually), since at this point I've been SMOKING when it comes to my theory that Imu would be a lot like Big Mom, but with Demons.
Always remember: the Fat Lady Sang at the end of Whole Cake... but she didn't sing at the end of Wano.
She ain't done, yet. Hoping Elbaph ends with another Linlin Musical number, they were really fun in the anime.