A combination of the two.
They are still being looked into, and by more serious people this time, and the government and just about everyone else involved except a few MPs who keep bringing it up, is trying very very very very very hard to pretend that it didn’t happen, and isn’t relevant. Corbyn is happy to assist the government in this.
Everything else you’ve said is also correct. Corbyn is the main problem here. Theresa is only still there because everyone knows she will “do a Cameron” not long after Brexit, and the hungry little Tory dogs like Gove, Johnson, and so on, are waiting for her to flee for the countryside so one of them can take her place, say she fucked it all up, swear he’ll fix it, and ride out whatever happens going “Oh no, pity Theresa fucked us so bad! Good thing I’m not her!”. Corbyn wants Brexit for barely-rational socialist reasons (I say this as a socialist, but like fuck me, sometimes you gotta go with the lesser of two evil, Corbyn, you dumb wanker, the Red Revolution isn’t going to happen Because Brexit - but Corbyn thinks it will), and I think he personally actually wants No Deal, because it would plunge the country into chaos, and he thinks Labour would do well out of that, because he doesn’t understand the demographics of his own country, nor does he understand recent history (in the post-97 era, Labour does well when the country does well - the Tories do poorly when the country does well - the more confident and happy people are, the more willing they are to support higher taxes, better benefits, and the less they’re willing to tolerate Tory crook-ery).
Re: a second referendum, the support is good, but it need to be overwhelming. You would probably need 60%+ of people in the country to support that to get it. I think that could be achieved very easily by shitting all over the result repeatedly and publicly, but it’s kind of too late for that.
Basically Theresa has played directly into the hands of the absolute worst scumbags in her party, and she knows she has, and I would argue that she has done so if not intentionally, then knowing full-well it was very likely. Because her government is such a shit-show, she’s also out of time.