I think they had various goals and hopes. I fully believe they hoped and intended to try and take a major Russian city, to do war crimes and use it as leverage to get Russia to cede back some of their land. I also believe they probably would have tried to do nuclear terrorism (and still may with a dirty bomb) if given the chance to permanently contaminate Russian land as a way of showing to the world what happens to those who resist US power and hegemony, a monument of suffering and torment to intimidate Russians and remind the rest of the world of what will be done to you if you resist the US.

And doubtless they hoped that after capturing a city (best case scenario but the Zelensky regime is full of messianic optimists) they would divert Russian forces from the front which would allow them to do a push-back of some sort and regain some initiative and land as well as being a morale boost and and setting the Russian front back.

I think probably they're killing some civilians, a lot, doing war crimes like SA on others, and probably kidnapping some amount to the back of the lines and into Ukraine to hold as hostages (who will be badly treated and abused sadly) to trade for troops or some concessions from Russia in the negotiations. So this is not without a horrible cost to Russia and the Russian people.

I find the author's dismissal of the nuclear disaster scenario kind of odd. These are not rational people with a sense of self-preservation or shame. These are fanatics whose strings are being pulled by the US who would almost certainly rather poison and make useless part of Ukraine for a century rather than let Russia have use of it. When looked at from the perspective of these people are nazi-loving fanatics who would shoot of their own foot to spite some Russians (and have done much worse to their country to spite Russians and be used as a battering ram by the west purely to their own detriment already let's not forget) led by a guy who will probably be killed if he doesn't appease the nazi fanatics who run the main intelligence agency by the way. And the fact the US is the one benefiting here and all this is for their benefit then long-term land denial in the face of losing seems incredibly on message. Let's not forget what they did with Agent Orange in Vietnam and here they have the benefit of plausible deniability, it won't even be the US that the world blames, they can say their puppets became unhinged in the ending days and they didn't tell them and weren't able to stop them and oh what a pity this land Russia now occupies that was once useful and valuable farmland is now horribly contaminated and rendered useless to them meaning American produce has less competition.