Well it wasn't clear to me whether my friend Arabus's statements on [haja] vs. [hajaa], etc. were restricted to Syrian Arabic or whether he meant that they applied to all Arabic dialects. I'm assuming it was the former, but since I had prepared a post on this anyway, I might as well post it for information purposes.
حياء and حياة are different in the spoken language because the accent is different in both (['ha.ja] vs. [ha.'jaa]), not because the final t is presarved in the second.
In this country, "7aya" means either حيا (as in rain) or حياء. If you say "el 7aya wil mot" here people will conclude you're Syrian or Palestinian.
Also I believe most people in the 19th century pronounced both words the same ['ha.ja] (as evidenced by proverbs and frozen expressions).The fact that حياة is widely pronounced today [ha.'jaa]/[ha.'jaat] is due to the increase in literacy.
In Syria, perhaps, but certainly not in Arabia. This also evidenced by our proverbs and frozen expressions, but in addition to that, our traditional poetry would be otherwise unreadable (metrically, that is):
دنّ الدواة ودنّ لي طلّحية || أرسم بمبريّ اليراع سْطورها
الله من عينٍ إلى ناموا الملا || قزّت لكن التوتيان ذرورها
متذكّرٍ عصرٍ مضى لي فايت || ما قلّطت فيه الوشاة سبورها
(17th century poem)
غدينا سْوَاة صْلَيْب يوخون بالقرى // حياة الوزى ما بي حياةٍ مريبة
وانا والمشاعيب العصاة على العدا // مشاعيب بَايّام اللقا ننتخي به
(18th century poem)
أياة خمسينٍ تعشّيهم الشاة || من زوبعٍ وضياغمٍ خالطينه
أيّاتهم وأيّاة خيلٍ مريحات || وجيشٍ يعزّل من وراها كمينه
بايْمانهم مثل الحوص المدلاّة || والريش من فوق الغلب مردفينه
***
بايْمانهم مثل المحوص المدلاّة || والريش من فوق الغلَب مردفينه
تلفي غلامٍ بالمدارك رماني || رمية حصاةٍ في هدايم خرابة
ياخوي عندي لك وصاةً مصيبة || تراها وصاةٍ تلمس العقل وتصيب
ترى وصاة أخوك ما به معيبه || يا صار أخوك مكمل العقل ومنيب
(19th century bedouin poetry)
Traditionally, Arabian Arabic treated the 'taa marbuuTa' essentially in the same way as Classical Arabic, except that, in the pausal form, it was common to keep the 't' when preceded by an aleph, i.e. اة. It's possible that this "-aat" form developed from an older "-aah" form (which also exists and is evidenced by the poetry). One thing is for sure, they never said anything like "حيا" for حياة. Otherwise, as I said, the poetic metre would not work, and we wouldn't have place names like التنهات in the middle of the desert (Yaquut has it as التنهاة) or a town called مرات even though it appears in the Classical literature as مراة or مرأة. The central square in old Riyadh is called الصفاة and it is pronounced الصفات (it's possible that people once said الصفاه, but never الصفا). If you look at
this small dictionary of traditional Najdi words you'll notice how almost all the words that, etymologically, should be spelled with اة are instead spelled with ات (a few are spelled with اة but none are spelled with ا alone). These are very old words: most of these words are completely unknown today.
So to summarise, in Arabia, words that, in CA/MSA, would end in اة are pronounced with "-aat" or "-aah" but never just "a." Perhaps the preservation of the 't' (in the pausal form) in Arabia was an innovation, but if it was then it is not a recent one by any means (it was already widespread in the 19th and early 20th century when the vast majority of the population was illiterate and probably long before then), and it would not have replaced an older "-a" form but rather a form "-aah" (again, only in the pausal form). It is not due to the influence of the literary language but rather in spite of such influence, i.e. it was part of the natural evolution of the dialect.