He's been captured and defeated before. It clearly doesn't work and look at how big of a threat he is.
If he isn't killed, he can always rise in power again.
You are just seeing it from one point of view, that's why
I could have used the same excuse with Crocodile re-taking alabasta for example after being freed...
Kaido WILL NOT get his satisfaction of dying in this war.. all the power he built over 25 years just for this war where he dies in it... he will lose that army/force, and still lives...
Coming back to attack Wano can be just ignored same way Croc turned away from Alabasta
Also, I believe many Yonko will participate in EoS war against WG led by Imu/Gorosei... I think Luffy as "Pirate King" will command many other Top Tier pirates as "their crowned King" to fit the title properly...
And I think in that war Kaido will die and meets his end and get that satisfaction
I also think that only top tiers with some dignity/honor will follow Luffy in that war as fellow pirates. Basically Kaido I believe has some honor in him regardless of his current villainous ways which I feel was caused by his past in Rocks pirates. (BB is excluded, dude has zero honor Lol)
I feel the idea that Kaido must die no matter what is very one sided way to look at things without giving other potential "growth/depth/developments" into account