、。
Since no reply came, May wrote to Bill again.
Literal
Reply [subject-が] didn't-come [because-ので], May [topic-は] Bill [to-に] again letter [object-を] wrote.
Another variation on the same pattern, now with named characters and こなかった (didn't come) instead of なかった (didn't exist). Using 来る for a reply frames it as something expected to arrive, a subtle shift in perspective from the existential なかった.