How sustainable would non-intervention be in the case of documented, verifiable escalation? Consider, for example, the scenario where Russians fire (tactical) nuclear weapons on major cities. I just don't see how you can rely on further economic pressure in that regard. Possibly the exception is if China/India and others then abandon Putin in that instance, but beyond that I don't see how you couldn't advocate for a no-fly zone at a minimum in that scenario.
I am sure that Nato leaders are considering military options despite their repeated insistence that they won't intervene in that way. This seems correct, for now -- any escalation from Nato's side can only be in response to further aggression from Russia -- but I would assume that there are some red lines, and I suspect that nuclear or even chemical weapons could be one.