Since the end of the WW2 we have seen the emergence of lots of new countries, and the trend continues to exist. Separatist movements and dissolutions continue to exist and periodically increase number of countries. At the same time, there were almost no cases when the number was decreased (unification or absorption). And even in such cases united countries didn't exist for long (e.g. United Arab Republics). This raises the question on whether the post-WW2 international system imply a constant growth of the number of countries or we may see a couple of mergers of states in future?
Not necessarily, but assuming the order holds the forcible reduction in number of countries by annexation should not happen. The ones that are at risk are those next to a superpower with ambitions - such as Ukraine and Taiwan. One of the few annexations that has stuck is that of Tibet, for example.
Many of the "new" states arose from the collapse of states that were put together after WW2 (especially in the middle east), or collapsing empires (USSR). Eventually this will stabilise.
So it's more a question of how likely states are to unify peacefully in a stable international order. This is not impossible, but it will be a slow process. Possibly the EU will eventually become a "superstate" union like the US.
Here's the big list of state mergers, both successful and non-.
Of the successful mergers since WW2, notable examples include Malaysia, Tanzania, United Arab Emirates, Vietnam, Yemen, and of course Germany. Among others.
On that basis, the answer to your question is No.