εἴ τι μάχης ποτὲ δεήσοι
it could be understood as both personal and impersonal, so how to distinguish between them?
It’s impersonal, “if there should ever be a need.” Contrast ὁ δ’ εἶπεν ὅτι οὐδὲν αὐτῶν δέοιτο, that you posted earlier, “he said that he had no need of them.” Note the difference between δεῖ (impersonal) and δέομαι (personal), both frequently with internal accusative (what you call an adverbial acc. I think). δεῖ μοι τι τινός :: δέομαί τι τινός..
thank you