I was wondering if/when someone was going to make a post like yours....I believe you missed the point entirely - HN does not always get it right and on many occasions hell banned people still make posts worth reading.
There are reasons why HN allows the "show dead" ability and probably none of those reasons have to do with people trying to punish themselves by seeing "abusive users'" posts.
If people are being banned when they shouldn't be, then that's the problem. Adding two levels of banning won't fix it. What next, somebody gets really banned and you want a way to reverse that so you can still see their stuff, but then it turns out that the "really banned" section is also full of crap so you need a third level?
If hellbanning is being abused, then that should stop. Adding a second banning mechanism doesn't seem like a useful fix.
I agree with mikeash here. If a hellbanned person still wants to remain part of the HN community, it's really not that hard to create a new account. Sure, sometimes they get it wrong, but the vast majority of the case, they get it right.
That means, that by you turning on dead posts, you are subjecting yourself to the 80% case where they get it right. If one of them is spamming with huge blocks of text, etc... well, you signed up for it in the low-probability case that one of the dead posts actually contained valuable information.
Keep it simple. Don't start adding multiple layers of hellbanning protection just to fix a low-probability edge case.
There are reasons why HN allows the "show dead" ability and probably none of those reasons have to do with people trying to punish themselves by seeing "abusive users'" posts.