The author of II Kings records, "Israel was carried away from their own land to Assyria, as it is to this day" (II Kings 17:23). That is, Israel was still in Assyria at the time this passage was written. To determine the approximate point in time to which the phrase as it is to this day refers, we need only determine the date of the latest historical event recorded in the book. That date will be the earliest possible date the book could have been written. That is, a historical—as distinct from a prophetic—book can be written no earlier than the latest event it records.
Chronologically, the latest event recorded in II Kings is the release of one of Judah's kings, Jehoiachin, from prison some 26 years after the fall of Jerusalem in 585 BC. This release took place about 559 BC (585 - 26 = 559). We know, then, that the phrase as it is to this day can refer to a year no earlier than 559 BC, which is a full 159 years after Israel's fall in 718 BC. Israel did not return to its homeland in 711 BC, but was still in exile at least 159 years after its fall. God's punishment of Israel lasted far longer than a mere seven years!
Searching for Israel (Part Seven): Seven Years' Punishment
Other Forerunner Commentary entries containing 2 Kings 17:23:
1 Kings 12:25-33
2 Kings 17:23