Was the silent 'e' in "nine" ever pronounced? In Old English, the word for "nine" was "nigon", with no 'e' at the end. But, in Middle English, the word for "nine" was written either as "nine" or "nyne". Was that pronounced /nine/ or /ni:n/?
Chaucer's Parliament of Fowls may have an example of nyne pronounced as a disyllable:
And after shewed he him the nyne speres,
(I think "shewed" is a monosyllable here, although I'm not sure.)
On the other hand, Chaucer's Troilus and Criseyde (written in iambic pentameter, so in general, five feet each composed of one unstressed syllable followed by a stressed syllable) furnishes an example of nyne pronounced as what looks to be a monosyllable before a word starting with a consonant:
A wonder last but nyne night neuer in toune.
(Book IV, line 588. Other editions give the first word as "Ek".)
I would expect a disyllabic pronunciation to be pronounced /niːne/ (or /niːnə/) rather than /nine/, since I don't see why the vowel in the first syllable would develop a different length based on the presence or absence of a following /ə/. (We know that this is not a word that originally contained /nin/ in Old English).
Since a pronunciation of nine with final /ə/ does not seem to be etymological, I'd speculate that it arose by analogy with the pronunciation of other words, like eighte. Here's an example of that word in Chaucer:
And by his eighte speere in his wirkyng
(The Franklin's Tale, line 572)
As The Middle English Compendium notes, it appears that Middle English had many competing spellings, among them:
nīn, nine, ninne, nien, nie, ni- & nighen, nighien, niʒen, niʒne, nighe, niʒe & nēen, neien, nein, nen & neghen, neʒen, neiʒen, neghe, neighe
Presumably the spelling "nine" ended up succeeding because it best reflects the modern pronunciation, given the rules for how other words ending in "-ine" are pronounced.