I would imagine Garp's death should motivate Koby to really start putting some work in and hardening his heart.
It seems likely it will happen too imo unfortunately as Kuzan who is now officially part of BB, owes a lot to Garp too, for saving his life at least once before and respects him a lot.
He's the Admiral closest to Garp, although Akainu seems to have based his fighting style on Garp, as well as his dog theme and they share a similar brash, gung ho, no nonsense, shoot first ask questions later attitude too.
I can see a similar moment of how Sasuke witnessed Itachi killing their parents/clan and especially Zephyrs death in Film Z.
I still feel BB will be truly sadistic and force Kuzan to kill Garp in front of Koby. This will be what makes Kuzan truly conflicted in himself and divisive as a character, a character defining moment by far.
Also character defining for Koby as witnessing both his and his fellow former Admirals mentor be killed by said former Admiral is going to be a truly traumatic, soul crushing, heart breaking moment and define what kind of man and eventual future Admiral he'll becom. Although he might just ascend to VA like Garp did and refuse promotions to Admiral like how Garp did and thus out of respect for him and to have as much freedom as he did.
Oda has been faking us out hard on deaths since post Marineford, except Ashura and Izo offscreen from what I remember. I guess Kaido, Big Mom, Orochi and Kanjuro too lol. Maybe Jack and Perospero too? I doubt it though.
But like Marineford, I think Oda is gonna really let our guards down by then, make things go too well and then suddenly Blackbeard does something absolutely heinous and crafty and forces Garp to let Kuzan kill him to spare Kobys life and thus forcing Kuzan to "show loyalty" and over Blackbeard by killing Garp too.
This is all assuming Oda will even do that ofc. I mean just looking at how he's handling Sabo the poor guy and what he did with Kibemon and Izo lol.
I also doubt Bartolomeo is any danger from Shanks and Odas just baiting us too as usual but we'll see.
There's also the question if Kuzan is undercover or not still and if its Sword related too or even Sengoku or amd Garp arranged this. Hell maybe he and Akainu arranged it during their fight?
For those who know Breaking Bad too, Garp really reminds me of
Hank, Mr Asac Shrader and I fear he's gonna get a similar treatment to him ultimately too.