I'm not so sure this is cut and dried. Couple of things. These 10 tribes for the most part were not following the Lord at the time they were overtaken by the Assyrians and I would guess most of them at the time of dispersion didn't give a flip about observances. They were not observing Sabbath or festivals at the time. The perverted the land and were worshipping foreign gods. Alot of Northern Tribers who wanted to serve the Lord migrated to the Southern Kingdom. We see evidence of a remnant of a tribe here and there but I don't think we can assume entire tribes traveled as a group to a certain part of the world and laid claim to a piece of geography. We'd be talking about caravans of tens of thousands. Again, I can understand seeing evidence here and there of decendants of the tribes of Israel but to make a blanket statement and say such and such tribe ended up in England, such and such tribe ended up in Japan etc., etc.,....don't make much sense to me.
As far as observances, you're largely correct with respect to the time. But all had not abandoned the observances and rituals which is why they survive today in the groups readily discernable as being of those tribes. One example: Naphtali still grows it's hair long, they still eat kosher, they still line the borders of their garments with a blue thread. They still tell the tales of the exodus and sing songs about it. Ect. That is the tribe of today. Had they surrendered their identity entirely, this could not be so today. But we are in agreement. As far as speaking for the entirety of the groups, that is not my intent. I'm speaking to individual cases where the main body of the tribe can be traced to as an organized unit. You'd likely be amazed at the organized numbers represented. We're not talking about small insignificant numbers. We're talking groups that exist in the millions esp in the case of Manasseh.
I could have written more detailed information, that wasn't my goal. I wanted a digest posted for everyone to get a feel for what is known and out there. Something more informative than I believe it was Quester posted earlier, and definitely more accurate than the summation I saw from dave that tried to coopt Aaron. If I were to summarize the misinformation, disinformation and outright spin that has occurred on this topic today, it would not paint a pretty picture for the other side. At least Dave admitted his error - something to his credit. But somebody has definitely made the mistake again of misunderestimating me. LOL