Eowyn, Eomer.....Their Lifespans?

[Nilpaurion Felagund]

To understand why those with Númenórean blood have or have not a lengthy lifespan, we must first understand what gave the Dúnedain such a lifespan in the first place.

. . . the increase in the Númenórean lifespan was brought about by assimilation of their mode of life to that of the Eldar . . . (UT II 3 - endnote 1)

Since the Eldar were already in decline wouldn’t it also mean that the famed Númenórean longevity of old would fade, too? And as is said by Faramir:

[Faramir: ]For so we reckon Men in our lore, calling them the High, or the Men of the West, which were Númenóreans, and the Middle Peoples, Men of the Twilight, such as are the Rohirrim and their kin . . .
[W]e [the Númenóreans] have become more like [the Men of Twilight], and can scarce claim any longer the title High. (LotR IV 5)

Would not the last distinction - the lifespan - disappear, too, in this assimilation of mode of life?