Many different items can disintegrate once used up.
All corrupt dragon equipment, dueling rings and games necklaces to name but a few.
There are 21 saradimin items on RuneScape.
Any item labeled as "corrupt" will disintegrate after using it for a fairly short time.
No.
about 100 to 500 years
The best items in RuneScape are Partyhats, Divine and Elysian Spirit Shields, and Christmas Crackers Moneywise.
There is no way to clone items on Runescape, this was however a commonly used scam to get players to give them items to supposedly clone, but they don't get cloned.
While on RuneScape PVP worlds, if you die, you only lose the items you are carrying, not those in your bank, never in RuneScape will a death directly affect your banked items.
No. They do not.
There is no way to duplicate items in Runescape. Although there was a bug once which did allow a person to duplicate party hats, this was quickly fixed.
No. You can lend items without being a member.
Only items obtained through quests.
There are several items in RuneScape which have "sheet" in their name. Please clarify which one you mean.