A direct conflict between the us and putin's regime means complete nuclear anihilation of many cities of russia and us (and nato). We are talking tens if not hundreds of millions of deaths.
From a internal russia political standpoint, if russia is not able to hold with its convential army the "new" (ahem...) boundaries (or "enough" of them), it could "wipe clean", and that "legally", any "front line" with tactical nukes (5/10->? MTs).
putin's regime could not care less about economic sanctions, that's clear now, and on this matter china may be involved soon, since china (the factory of the world) will probably be caught providing some goods to russia. In one of the main contexts of "hacker news", for instance, their new 7nm electronics.
This conflict is now at a pivotal point, it all depends on what the ukrainian army and pro-ukrainian ppl of the "new" russian regions will do in the next weeks/months (this may be the beginning of a "pause" in the conflict, who knows).
That said, if I were a member of wagner PMC, whatever is my location in the world, I would get the first flight to russia...
Usage of nuclear weapon in any capacity will be not tolerated by US.
US has directly told to Putin what will be the retaliation. This means that the retaliation will be something that US believes will deter Putin to use a nuclear weapon.
It is obvious that nothing but military destruction will intimidate Putin, so it can't be anything less than that.