I think Nypa can survive in mangrove in inlands also where tidal waves are frequent. Global Invasive species database says

"Nypa fruticans (nypa palm) inhabits estuarine habitats from Sri Lanka to the Ganges delta to the west Pacific. It grows up to 10 m tall and produces large buoyant propagules that are dispersed with ocean currents. It was intentionally introduced to Nigeria, and has since spread to Cameroon. In the Niger Delta it invades deforested and exposed mudflats and forms dense monospecific stands which outcompete native mangrove species. The lack of stilt roots, absence of leaf litter and dense structure reduce estuarine habitat and may negatively affect native biodiversity."

Nypa fruticans occurs in Suderbans,  which is the largest mangrove ecosystems in India. These populations grows near the edges of the channels and creeks further it makes a homogenous  patches. 

Thank you

 Nypa prefers river alluvial soil  and can be  found along the edges of the stream/ river

Nypa fruticans prefers lagoons and estuaries. They have found predominantly in tidal forest systems in Andamans, which is interesting system not only based on its habitat specific but also taxonomically that it is monotypic to the subfamily Nypoideae of Arecaeae.

Very good fossils of Nypa available from Maastrichian and Oligocene period of Eurasia.

In Tanzanian estuaries, there are palms thought by some to be N Fruticans, that occur about 4-6 km inland along the river on the banks, where the water is brackish and not seawater saline. It is likely that these palms have evolved to dominate this brackish niche, where they outcompete mangroves. They can also utilize a freshwater (rain derived) pool of water in the soil that exists above the brackish groundwater.