Is there a word used to describe items that would need to be replaced over time (either due to wear and tear or just regular usage)? It would be similar to "perishable" in regard to food products, but for mechanical parts, etc...
You might try "consumable", which is defined by oxforddictionaries.com as "a commodity that is intended to be used up relatively quickly". That site offers this as a usage example:
...[this brand's] printers benefit from years of heritage and the relatively easy availability of consumables.
In some contexts, and as your question implies, these would be called wear items. Auto headlamps and hoses, etc, are usually excluded from warranty because they are expected to eventually wear out.
In a different context you have consumables, not that these are expected to fail, only to be replenished in the course of use. Copier toner is a consumable.
Disposable is the usual term in Britain.
Perhaps you can use "nondurable goods"
goods that remain usable for, or must be replaced within, a relatively short period of time, as food, apparel, or fabrics
as opposed to "durable goods"
goods, such as most producer goods and some consumer goods, that require infrequent replacement. Compare disposable goods, perishables Also called: durables
Serviceable [Dictionary.com definition 3]
capable of being used, worn, cleaned, repaired, etc., easily.
'The serviceable parts include brake pads, clutch plate...'
sacrificial, sac·ri·fi·cial, adjective —Google
designed to be used up or destroyed in fulfilling a purpose or function.
Galvanic anode —Wiki
A galvanic anode [protects metal structures from corrosion].
They are made from a metal alloy with a more "active" voltage (more negative reduction potential / more positive electrochemical potential) than the metal of the structure. The difference in potential between the two metals means that the galvanic anode corrodes, so that the anode material is consumed in preference to the structure.
The loss (or sacrifice) of the anode material gives rise to the alternative name of sacrificial anode.
sacrificial part —Wiki
A sacrificial part is a part of a machine or product that is intentionally engineered to fail under excess mechanical stress, electrical stress, or other unexpected and dangerous situations. The sacrificial part is engineered to fail first, and thus protect other parts of the system.
electrical fuses, over-pressure burst disks, mechanical shear pins, galvanic anodes, ect.
Welding rod is a consumable. The fuses protecting the welder are sacrificial. The holes in your gloves are to be expected as most PPE has a finite lifespan and requires daily inspection.
Things Fall Apart —Chinua Achebe, 1958
As Eric said above, I think 'replaceable' implies that the piece will need replacing at some point. Also,'long-lasting' suggests that the item does ultimately come to an end (I can't comment yet, thus the answer).
Unrepairable I can't think of anything that won't wear out over time. Friction and erosion -- "wear and tear" can be reduced, but can never be eliminated. But things used to be much more repairable than they now are, and part after part could be replaced. It is now impractical to repair many things, so people just throw them away and buy a new item. When was the last time you called a TV repairman? Repair: "To restore to a sound or good state after decay or injury. To remedy, heal or mend." Webster's New Collegiate. Thus, unrepairable is "Not capable of being repaired"
"depreciable" or "depreciating" may work
In computer science, we use the word "Transient"