Many scholars would put the timeframe as 722-718 BC. They never returned and became known as the 'lost 10 tribes' of Israel.
Negro'of the 10 tribes of Israel
The tribal arrangement in Israel was based on descent from the 12 sons of Jacob. These twelve family heads produced the "twelve tribes of Israel." Two Tribes made up the Northern Kingdom of Isarel, Judah and Benjamin. The other 10 Tribes made up the Southern Kingdom of Israel. 1 Kings 11:29-38
The ten tribes of Israel were scattered by the Assyrian Empire during the 8th century BCE. Following the conquest of the northern kingdom of Israel in 722 BCE, the Assyrians deported many Israelites and resettled them in various regions of their empire. This event led to the tribes becoming known as the "Lost Ten Tribes of Israel," as they were largely assimilated into other cultures and lost their distinct identity over time.
Israel, which had been a confederation of the Israelite tribes under the Judges, became a kingdom when the Prophet Samuel anointed Saul as its first king. See 1 Samuel ch.8-10.
There were 10 tribes, but they weren't lost. What happened was, during the Babylonian captivity of 586 BCE, the 12 tribes of Israel were expelled from the land and sent to Assyria. After 70 years, 9½ of those 12 Tribes had just assimiliated into Babylonian society, leaving only 2½ tribes returning to Israel.
The Assyrians
The 10 tribes of the Hebrews are known as the lost tribes because no one knows what happened to them.
The faith of the Israelites became known as Judaism. This is because, though the entire nation was known as Israel, but Rehoboam broke away and called his own kingdom Israel, taking 10 of the original 12 Israelite tribes with him. The two tribes left in the south were Judah and the tribe of Benjamin, the far larger of which was Judah, so the southern kingdom came to be known as such. Therefore, those living in Judah, were called Jews. After the Babylonian exile, the kingdom of Israel to the north was dispersed, and the 10 tribes of that kingdom were lost, leaving only Judah to carry on the Israelite faith. Thus, the only people left who believed in the God of Abraham were those from Judah - Jews. Accordingly, the religion they believed in was called Judaism.
The people of Germany migrated to Europe from the middle east after 721to718 bc . At that time they were know as Assyira, and they had taken into captivity with them the northern 10 tribes of Israel. This can be found in 2 kings 17:6 in the Bible. The 10 tribes soon lost there Identy, thus they are know as the lost 10 tribes of the House of Israel.
The Assyrians, under King Sargon II, deported the ten tribes of the northern kingdom of Israel in the 8th century BCE. This event is commonly known as the Assyrian Captivity.
After King Solomon's death, Israel separated into two Kingdoms - the Northern Kingdom of Israel which consisted primarily of 10 of the 12 tribes of Israel, and the Southern Kingdom of Judah which consisted primarily of tribe of Judah and Benjamin. It should be noted however, that each Kingdom had members of all 12 tribes of Israel.