Page 146 in the Players Handbook is the only source I can find that mentions anything regarding arrows being destroyed or used up, in general.
Many weapons have special properties related
to their use, as shown in the Weapons table. Ammunition. You can use a
weapon that has the ammunition property to make a ranged attack only
if you have ammunition to fire from the weapon. Each time you attack
with the weapon, you expend one piece of ammunition. Drawing the
ammunition from a quiver, case, or other container is part of the
attack. At the end of the battle, you can recover half your expended
ammunition by taking a minute to search the battlefield."
As for arrows disappearing and being used up because of wear and tear, I see no actual rules for this. You could assume that half the arrows you don't find were arrows that broke off during the fight, or were too damaged to reuse.
The answer to your questions, in order of your:
- "Is ammo reusable and recoverable" Yes
- "Is there any guidance on how long an arrow/bolt/dart should last,
- "In the absence of RAW guidance, can someone suggest a mechanism for
ammunition recovery...." Other than using the RAW, as shown, it might be
easier to talk to your players and see if they would like to do this
A game feature to consider for increasing spent arrow harvesting: the cantrip, Mending, used by Bards, Sorcerers, Wizards, Clerics, and Druids. (PHB p. 259)
Mending is something I would allow a player to use to recover a few extra arrows as well, but not all of them. Technically the RAW guidance on how long arrows last. Statistically (based on recovering arrows at 1/2 usage rate) they're going to break after 1-2 shots, after which they become unrecoverable either because they are lost or broken. Mending can repair a mundane item like an arrow. ~From a comment by @Randomorph