I'd keep the Twitter profile, even if its inactive, just in case.
I've found that some cross-promotional opportunities require a mailing list, an FB page, and a Twitter profile. (In other words, participants are expected to publicize the promotion through all three.) I've yet to run across one that required any other social media accounts, but those two are fairly commonly required.
Also, Twitter is good for some things. For instance, if you do Amazon giveaways, publicizing them on Twitter with the hashtag #Amazongiveaway produces a huge response. I've also noticed that in general, since the latest round of Facebook trying to strangle any kind of organic reach, I usually get more response to promotional posts on Twitter than I do on FB, even though my FB following is more than three times as large.
I don't spend a lot of time looking at my Twitter feed, so I don't really notice the toxicity as much. And I think the risks of getting a Twitter mob raging against are relatively low. Frankly, I'm not a big celeb (or a celeb at all, really) to attract the attention of potential nut jobs. I think most indie writers are that way. If I stick to promoting books and furnishing other tweets that are entertaining or informative (but not too political or otherwise controversial), I think the danger is minimal.