Maybe Jack was using high quality artist's paper.

If the Titanic were laying in a shadow zone, organic matter would decay more slowly. Very deep parts of the ocean feature very little oxygen which speeds up decay, and the Titanic is resting very deep.
It is easier to build strong children than to repair broken men ~ F Douglass

Paper has been recovered from the wreck including money and never mailed letters etc. they have been on display in many Titanic artifact exhibits. According to scientists and explorers, paper can survive for many years underwater if it is protected especially by leather or certain metals. The money and letters recovered from the wreck have either been found in leather suit cases and wallets. Jacks drawings were in a leather bound portfolio and locked in a metal safe so it had extra protection. My question is more of would the charcoal still be on the paper or remain that clear after all the time? Brock even rubs the date with his finger. The drawing is not smudged at all!

Thanks for that explanation.

Paper is made from trees, and wreckage from wooden shipwrecks that predate Titanic can still be found in the oceans
I guess it would depend a lot on the quality of the paper, the conditions of the water, the weathering from ocean currents, and any marine life that want to eat it
I seem to recall that there is at least one WWII wreck, I can't remember the name, that still has visible papers in the shelves of a desk of one of the officers And that was no more than 33 years, after Titanic sank.
EDIT:
I just remembered that Paper Money has been salvaged from Titanic.
Being inside a wallet or in a binder or in a safe would keep paper in better condition a lot longer
Jack's drawing of Rose, surviving intact all that time, was probably 100% possible.
But it would most likely be very fragile, and would require extreme care in handling it, in preserving it, to be able to eventually display it in a museum.

Jack's book of drawings is made of magic.
http://www.youtube.com/user/pumpkinman4ever?feature=mhum