Article 5 is nothing but words which could be broken in the same way.
Let's consider Article 5. It states that in case of armed attack each party "will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area."
"assist .. by taking .. such action as it deems necessary". Surely, some parties could claim they don't deem necessary sending their help into a fight they don't want to be a part of.
No reason to believe Russia will stop so long as counties signaling intent to let them continue.