Does having the led brightness set to max always, reduce the lifespan of my keyboards led?

Also does deck offer an extended warranty?

Having the brightness at the maximum level will not reduce the lifespan of the product.

Deck does not offer an extended warranty.

Another question, on my old non mechanical keyboards when I would use one key more than another (such as ASWD) eventually those keys would wear out. So my question is, say I use the A key more than any other key, will that key eventually wear out first and thus I will have a working keyboard without an A key?

BTW I received my deck keyboard, it is truly amazing.

The key switches we use have a life cycle of 50 million actuations so to kill one of these is much harder than your off the shelf keyboard. If in fact you wear out a key, to get the worn-out key to work again you would then probably replace the switch (unlike a cheap membrane keyboard where there is no way to service a dead key).