I, too, dislike the ever-present possibility of me being banned and not knowing it, causing me to waste time writing earnest comments that go into a black hole. I’ve thought of a change that might assuage fears like mine while still allowing you to use hellbans to deter trolls: using separate types of bans depending on the likelihood of a user’s troll-ness.
I don’t have any data about trolls, but perhaps if you looked at your data you might find that people rarely turn into trolls if they have at least a certain amount of karma points, or if they have been on the site for at least a certain amount of time. If you find such a pattern, you could make it so that when those users write a trollish comment and should be banned for it, they are actually informed of the ban instead of silently hellbanned. But if you ban a user whose karma or time-on-site suggests a higher chance of being a troll looking for a reaction, you can still hellban them silently.
This policy would mean that long-time users would know not to fear hellbanning after they pass the publically-stated point. It would let them interact with the site without that slight fear that their comments are going to waste, because they know the site would visibly prevent them from writing comments if they’ve been banned. But the policy would still let you use hellbanning, which is supposedly very effective, as a deterrent for trolls. I hope that there actually is a correlation between likelihood-to-be-a-troll and some combination of karma and account age that you can base this policy on.