Dunno, from the looks of it the navy mostly mobilized mitilia against the former shichibukai. It almost sounds like a reach that the marines would have the capacity to send the folk they actually needed to deal with the former shichibukai. Mihawk, hancock, weevil, buggy...
It's getting increasingly likely that mihawk is straight up a yonko level fighter. Since the plot pretty much requires that as zoro just learned conqueror cladding and his actual output from all of his swords can be reasonably estimated to be potentially deadly to actual yonko. He definitely lacks haki volume though.
Both hancock and weevil have been praised by relevant people at least. Sengoku was relieved to have hancock join the great war and weevil was acknowledged as powerful by kizaru. I think it's fair to estimate admirals wouldn't have an easy time with either at least.
And then buggy. It's all speculative but I think his position is really good right now... Buggy is obviously quite weak, last we saw him not even a haki user. But his unearned hype has allowed him to amass an extraordinary amount of followers. Probably not exceptionally powerful followers but still a lot. Enough to secure his place in the new world. From ID he got hundreds of followers from many floors. And his forces probably increased in number and strength during his new world tenure. It's by no means a stretch that buggy's forces number in the thousands. While buggy probably didn't have commander like figures during his tenure as shichibukai, his militia probably was envied by actual yonko.
So.. who do you send to deal with them? We know militias in the story are important so dealing with any of them would require significant resources. And we know the marines were stretched thin before the shichibukai were disbanded. I think the world government will half ass this out of sheer inability to send the appropriate amount of forces to deal with any of this individuals.
Like I said before, I'm arguing merely from a narrative perspective.
Is it possible that the Shichibukai all escape? Yeah, if the marines send a bunch of fodder, no doubt the Shichibukai will all escape. Would this scenario make the narrative any interesting? I'd argue no. Does it make logical sense to send a bunch of fodder after the Shichibukai? I'd argue no for that as well. If I were Akainu, I would have at least 1 or 2 admirals involved in the operation?
We also have something from Oda himself, where he implied something has happened to Sabo, Vivi and Boa.
Some other narrative points:
- SSG: Is the SSG, which was mentioned as a direct replacement of the Shichibukai, not going to demonstrate why it is so?
- Coby going after Boa: Would Oda have Coby go after Boa, just to take an L? I doubt it, especially given how Coby has been getting built up
All the Shichibukai were considered important for the WG during Marineford. This doesn't really mean much.
If Marines ABSOLUTELY want to capture the Shichibukai, they certainly can. Even Mihawk, just send a couple of admirals after him. Nobody in the series is soloing 2 admirals.
Yes, they are stretched thin. But, after abolishing the Shichibukai system, what else takes precedence over capturing them? They should focus most of their power on capturing them. Note: the entire stuff with Wano arc happens a few weeks later after the abolishment.
Let's look at the Shichibukai themselves:
- Mihawk:
Like you said, most likely Yonko level. Being Zoro's endgame is just one reason, but not necessary. He's been portrayed with Shanks, who is a Yonko himself. Given his power and narrative roles, least likely to get caught
- Buggy:
Was amongst my picks for those who could be caught, but now confirmed to not be the case, considering he did some wack stuff that made him a Yonko lol.
- Boa Hancock:
She's at best as strong as Doflamingo, which itself is giving her major benefit of the doubt, given how weak her crew is. I mean, her 2nd and 3rd strongest members (the sisters) got solo'd by pre timeskip Luffy. Assuming she's as strong as Doflamingo, any admiral can low diff her. The major flag for her however is that Coby is after her, Coby has the blessings of Oda. As well as Oda's own foreboding words.
Most likely candidate to get caught.
- Weevil:
Massive wild card. Apparently very powerful. I don't see him being captured, because then what is the narrative point? Introduce this random dude and get him caught before doing anything with him? Maybe, if Oda wants this dude hulking around and making trouble in the prison, just unlikely IMO