The treaties comprising the Peace of Westphalia contain many clauses. Most were invalidated since then. Is any of the clauses still legally valid? If not, when was the last of them invalidated or replaced?
You are putting it in a framework governed by law. However, the context of international relations is chaotic and not governed by any laws other than strength (in its various forms, cultural, economic, military).
International laws such as the Treaty of Westphalia are then just some form of contractual agreements valid until the agents decide to not honor them anymore. At a later stage, they may become part of doctrine and become precedents for the resolution of future disputes (in a mechanism similar to common law).
In the specific case of the Peace of Westphalia treaty, if you read the text, you can see that it is actually comprised by many agreements regarding small portions of sparse territories assigned to vassals, therefore among the years I think that technically they have taken full effect, and therefore the law can actually be considered valid.
Of course, if at a later stage other treaties affect these territories, while the law is still valid (it has taken its full effect), the new laws supersede the first one, marking the historical evolution of societal organization.
While not necessarily directly applicable, the Peace of Westphalia is frequently attributed as the source of a conceptual Copernican revolution in international affairs in which legal authority of divided between sovereign nation states that each have a particular territory which other sovereign nation states respect in the absence of good cause to do otherwise.
Before that time, authority over particular people and places was seen in more of a feudal and personal network of relationships of particular living leaders, rather than as a comprehensive system of sovereign states.
This concept, sometimes called Westphalian Sovereignty, is embedded deeply, sometimes explicitly and more often, reading between the lines, in almost all modern treaties and in international affairs more generally.