I have read how you mention that the Ishmaelites have "dissapeared". Can you assist in defining how this came about ?.
Did they actually dissapear all together...ie extinct/died out, or have the descendants of Ishmael branched off to such an extent that the waters are to muddy to follow them or who they are today ?.
I had pretty much parroted what many say about Arabs being the seed of Ishmael, until I read Dr. Amari's book. I want to enter portions of a chapter when I get a chance that answer to exactly your question.
The 12 tribes from Ishmael's sons inhabited the norther Sinai and into the top corner of NW Arabia and if anything moved up into the fertile crescent from there. They wound up inhabiting an intersection of 3 trade routes that appealed to the Arabs who moved in around them and so they were either absorbed by them or exiled by them. There OT eventually falls silent on the Ishmaelites.
God said that he would bless Ishmael and make him a great nation, although we all know he has no part of the promise for Israel. But he did say he would prosper greatly and be un-numbered like sand (or something like that).
Gen 22 15
And the angel of the LORD called unto Abraham out of heaven the second time, 16 And said, By myself have I sworn, saith the LORD, for because thou hast done this thing, and hast not withheld thy son, thine only [son]: 17 That in blessing I will bless thee, and in multiplying I will multiply thy seed as the stars of the heaven, and as the sand which [is] upon the sea shore; and thy seed shall possess the gate of his enemies; So that was a promise to Abraham and his seed, which, since the covenants are passed to Isaac would apply to his seed.
Gen 17:20
And as for Ishmael, I have heard thee: Behold, I have blessed him, and will make him fruitful, and will multiply him exceedingly; twelve princes shall he beget, and I will make him a great nation.Gen 16:12
And he will be a wild man; his hand [will be] against every man, and every man's hand against him; and he shall dwell in the presence of all his brethren.Regarding the seed of Ishmael and the 12 tribes, at one point the OT describes them as being as numerous as locusts, and as being quite cantankerous, but then having disappeared from scripture this may be previously fulfilled prophecy.
If you ever need to do a search (like "sand" that I just used to recover that verse) or phrase or something these are my favorite links.
This one is KJV by default
http://www.blueletterbible.org/This one has Strong's definitions and Greek-English interlinear, but unfortunately it is NKJV by defaust (but easy to switch)
http://www.olivetree.com/cgi-bin/EnglishBible.htm