- Είπε το(ν) "He told him". Obvious error for Είπα το(ν) "I told him". I'm going to take the clitic on face value as accusative, confirming that whoever told degli Uberti about how a Macedonian peasant might speak was from the north of Greece. (The proto-Bulgarian inscriptions has accusatives replacing datives, and the xi AD church deeds of Southern Italy have genitives, so we know the isogloss between accusative and genitive indirect objects was already in place.)
This might instead be "He said the [following]", with the το an article introducing the following clause. But while articles can introduce nominalised quotations (Το πολύ το Κύριε Ελέησον κι ο παπάς το βαριέται "Even a priest gets sick of too much 'Lord have mercy'"), that would be pretty forced here.
George adduces ηξεύρω from Cappadocia, for which my thanks. I remember my own Cypriot grandmother saying δεν ηξέρω γιέ μου, and I've only just clicked their initial /i/ is likely related.
I think my argument that μετά χαράς is contemporary diglossia and not a fossil is weakened by the fact that we clearly do have such prepositional genitive fossils elsewhere. I'm thinking of από σπέρας "since last night, overnight" and από βδομάδας "from next week". Morphologically they are entirely vernacular (Ancient Greek would have had ἀφ’ ἑσπέρας and ἀφ’ ἑβδομάδος), but they just as clearly have a prepositional genitive; and their vernacular phonology makes it clear they can't have been borrowed from archaic Greek, either in 1300 or 1800. (There's a whole family around the former expression in Early Modern Greek—Kriaras s.v.—showing people trying to grapple with it: αποσπέρα αποσπερί αποσπερίς αποσπερού αποσπερής).
My argument for μετά χαράς being diglossic boils down to intuition over it being a politeness formula—something that archaic Greek speakers would have kept using. But there's no elided vowels as in από σπέρας to confirm how nativised μετά χαράς was.
Trust George to do the relevant TLG search, and that does in fact weigh more towards it being just vernacular, and thus just a fossil: Cantacuzene's letters to the sultan were in Demotic, and the Saints' Lives did indeed make concessions to the vernacular. My lame response is, any spoken form of High Greek would have been closer to Koine than the fake Thucydides of the historians, so μετά χαράς could well still have been learnèd. But I'm not sure, given the distribution George reports.
The similar expression George mentions is μετά βίας "perforce", again with a prepositional genitive. Kriaras s.v. βία 4a gives quotations in Early Modern Greek of both the archaic μετά βίας and the partly updated με βίας (in Libistros); the latter is a nativisation of the preposition, which like από σπέρας suggests productive spoken use. Btw George, why'd you think it less likely to have been colloquial?
I have no recollection of the examples of μετά χαράς, although I recall I was on the lookout after discovering Dittamondo. Given how half-baked my conclusion about μετά χαράς was in the previous post, I'm not sure I should have published anything on it. :-) At any rate, for better or worse (and it is for worse in most ways, except for googlability), this is where I publish now...