Καὶ ἐγένετο ἡ πόλις ἡ μεγάλη εἰς τρία μέρη, καὶ αἱ πόλεις τῶν ἐθνῶν ἔπεσον· καὶ Βαβυλὼν ἡ μεγάλη ἐμνήσθη ἐνώπιον τοῦ θεοῦ, δοῦναι αὐτῇ τὸ ποτήριον τοῦ οἴνου τοῦ θυμοῦ τῆς ὀργῆς αὐτοῦ.
If τὰ δύο μέρη means 2/3, τρία μέρη means three quarters (3/4) etc., so could ἐγένετο ... εἰς τρία μέρη be understood as "with a loss of one quarter (1/4) of her population (or area)"?LSJ μέρος wrote:IV. part, opp. the whole, “ὡρέων τρίτατον μ.” h.Cer.399, etc.; τρίτον κασιγνητᾶν μ., i. e. one of three sisters, Pi.P.12.11; “μέρει τινὶ τῶν βαρβάρων” Th.1.1; τὰ δύο μ. two-thirds, ib.104, Aeschin. 3.143, D.59.101; “τρία μέρη . . , τὸ δὲ τέταρτον” Nic.Dam.130.17 J.; οὐδὲν ἂν μέρος οὖσαι φανεῖεν τῶν . . no fraction of . . , i. e. infinitesimal compared with . . ,
I understand that τρία μέρη . . , τὸ δὲ τέταρτον quoted in LSJ above means "3/4 ... 1/4", and that unambiguously the authour of Reveleations uses τὸ τρίτον in other places to refer to the third that is killed or lost, i.e. δύο μέρη (2/3) were not lost or killed.
The syntactic parallel that BDAG refers to is:
Josephus, AJ 1,172 wrote: ἐπὶ τούτους στρατεύσαντες Ἀσσύριοι καὶ μέρη τέσσαρα ποιήσαντες τῆς στρατιᾶς ἐπολιόρκουν αὐτούς: στρατηγὸς δ᾽ ἑκάστοις ἦν εἷς ἐπιτεταγμένος. γενομένης δὲ μάχης νικήσαντες οἱ Ἀσσύριοι φόρον ἐπιτάσσουσι τοῖς Σοδομιτῶν βασιλεῦσι.