No, salt itself doesn't spoil or expire in the same way that perishable foods do. However, the longevity and usability of a salt block depend heavily on its type and how it's used and stored.
Himalayan Salt Blocks & Cooking
Cooking on a salt block that hasn't been heated properly will degrade the block faster and over-salt your food. [Cooking on a salt block that hasn't been heated high enough will not only over-salt your food, but it will also degrade your block much faster.] Even with proper use, surface degradation is possible, and the top layer might need to be shaved off with a grater or microplane if it becomes excessively dirty. [It's salt, so really you can just use it as salt, if it's super nasty on the surface you should probably shave off that with a grater or microplane.]
Livestock Salt Blocks
The lifespan of salt blocks for livestock varies considerably. Factors such as weather exposure (rain and snow), animal usage, and the block's quality influence how long it lasts. Some blocks might last for years, while others can disintegrate quickly. [They vary in durability. I've used them for years. Most of them seem to last forever and others disintegrated quickly.] Blocks kept dry and protected from the elements last longer. [I have them up off the ground on stone blocks and under cover so they wont get wet. The goats do jump on them... which obviously isn't ideal] [Depends on how much rain we get. They typically last about 6 - 8 months for me. Less if there is a lot of snow.] [Yes, salt licks can be left outside. Of course they will dissolve in water, but usually tend to last well enough in average rain.]
Other Considerations
Some formulated mineral licks, like those specifically designed for animals, might not have an expiration date if stored correctly and remain uncontaminated. [The 'Vitalic Nutritional Loose-Mix Lick for Animals' by Nutrimol (formulated to Pat Coleby's specifications) doesn't expire.] However, even with these, observation for signs of contamination or degradation is advised. Similarly, Himalayan pink salt, while naturally occurring and ancient, might have an expiration date on its packaging primarily due to potential contamination concerns during handling and storage. [There are a number of things common to kitchens that just don't expire as long as they are stored correctly and aren't contaminated by outside sources.]
