Most brands have what I call the stupidity clause written into their terms. Normally they call it 'player error' or similar and they spell out that the warranty doesn't cover damage caused by insufficient preparation, or from damage caused by driving at yorkers etc.
We warn all local buyers not to use their bat at club nets as almost all the nets in Peterborough are pretty low bouncing. We don't say 'you won't be covered' but i suppose we are implying it.
I am yet to encounter a brand who has actually enforced the 'player error' clauses i laid out above. Most agree to repair/replace and then provide a letter/email to give to the customer outlining how willow is a natural product, needs preparing correctly and cannot be expected to survive when playing aggressively at certain deliveries etc etc.
I have heard of certain retailers who won't entertain a warranty claim if you bring the bat back within 2 weeks of purchase, as this is apparently how long it takes to knock a bat in. Quite an inventive way to avoid fulfilling your after care obligations if you ask me