Did monitors replace river gunboats?

Did monitors ultimately replace river gunboats during the world wars?

No. Monitors were one form of gunboat, while sloops increasingly handled diplomatic gunboat duties and motor gunboats carried the combat label forward.

The answer separates ship function from naming convention. A monitor could perform gunboat work, but the broader type did not disappear when monitor construction declined. Sloops inherited much of the overseas presence role, while fast motor gunboats became a distinct wartime expression of the same small-ship fire-support idea.