You will come across different warranties for bathroom wall tiles. Five years or so is the least you should expect. There are many brands that offer ten years of warranty but only on material or manufacturing defect and labour, which covers professional installation by a licensed and certified technician. Very few companies offer over ten years of warranty. Ten years or so may seem to be enough but the durability should not be assessed accordingly.
Bathroom wall tiles are installed as dados or backsplashes. They do cover a much larger space than the backsplashes in the kitchen. They serve as more functional dados than the wall tiles you may have in your living room or perhaps in your bedroom. Tiles on the bathroom floor are exposed to more water, dust, organic matter, residual traces of soaps, shampoos, gels and creams among others, grime build-up and moisture than those on the walls. The tiles on the walls must be moisture resistant. They may also be waterproofed. They will have to deal with spills and whatever gets splashed around but they do last longer than the files on the floor.
The ideal durability of bathroom wall tiles will depend on the choice of material and the quality of the finished product. Twenty years is the last you should expect. There are many types of tiles that look good on bathroom tiles even thirty years after they were installed. Regular cleaning and timely maintenance is the key to retain the aesthetics. You may have to deal with the odd and rare repairs. A tile or two may always get damaged or become less pleasant to look at. These are not major issues. Expect twenty years or more. The most expensive bathroom wall tiles can last fifty years and at times longer.