How many times will God pull us out of darkness, out of slavery, out of exile, and restore us to fullness of life?
We know of this person from the books of Ezra and Nehemiah. Ezra seems to have swept in like a second Moses with perhaps the same effectiveness. The book of Ezra ends rather abruptly with a very specific list of those who transgressed some derivative law, and really has no resolution. Some scholars believe that the books of Ezra and Nehemiah are one work, following from 1 and 2 Chronicles, so it may help to read them all together.
Ezra travels back to the promised land, rebuilds Jerusalem and the Temple, and calls the people to renewed adherence to the Covenant. The people promise to reform but, as the end of the book appears to indicate, it seems like - as usual - it did not last long.
So I guess the answer to the first questions is "forever" and that is because it is we who fail, not Him for He is faithful forever.
In the first year of Cyrus, king of Persia, in order to fulfill the word of the LORD spoken by Jeremiah, the LORD stirred up the spirit of Cyrus king of Persia to issue a proclamation throughout his entire kingdom, both by word of mouth and in writing: “Thus says Cyrus, king of Persia: ‘All the kingdoms of the earth the LORD, the God of heaven, has given to me, and he has charged me to build him a house in Jerusalem, which is in Judah. Those among you who belong to any part of his people, may their God be with them! Let them go up to Jerusalem in Judah to build the house of the LORD the God of Israel, that is, the God who is in Jerusalem. Let all those who have survived, in whatever place they may have lived, be assisted by the people of that place with silver, gold, goods, and livestock, together with voluntary offerings for the house of God in Jerusalem.’”
After these events, during the reign of Artaxerxes, king of Persia, Ezra, son of Seraiah, son of Azariah, son of Hilkiah, son of Shallum, son of Zadok, son of Ahitub, son of Amariah, son of Azariah, son of Meraioth, son of Zerahiah, son of Uzzi, son of Bukki, son of Abishua, son of Phinehas, son of Eleazar, son of Aaron, the high priest— this Ezra came up from Babylon. He was a scribe, well-versed in the law of Moses given by the LORD, the God of Israel. The king granted him all that he requested, because the hand of the LORD, his God, was over him.
Ezra had set his heart on the study and practice of the law of the LORD and on teaching statutes and ordinances in Israel.
-- Ezra 1:1-4,7:1-6,10