The life of brake pads depends so much on particular use it isn't really possible to give a mileage. Having said that, 26k mls doesn't sound unreasonable to me, and if they are down to 2 or 3mm I'd change them personally, just as I wouldn't run tyres down to the minimum legal tread depth. They start off at something like 6 or 8mm so you've had most of the use out of them. If the car spends all its life on motorways they'll last many times as long as if it does all its miles around town for example.
Most garages will try to get business if they can, they are businesses after all, advising the pads are well worn seems pretty reasonable and responsibe even, if that's actually the case. It depends whether you trust them. Some will of course try it on, others will be genuine.
It's worth checking that the calipers are working correctly, pistons not seized and caliper free on the sliding pins.
The ratio of pad to disc wear depends on a lot of factors, the ones I've changed recently have tended to go as a set, there was a time when discs lasted for ever but not so much with modern brakes. Infrequent use tends to result in disc corrosion which can end up with braking surfaces reducing dramatically. I recently changed a Mini rear brakes which are prone to problems and the discs were in a terrible state, how it passed an MOT two months earlier is beyond me. I have no idea how old/mls they were. The pads had quite a decent amount of material left. What do you all reckon, needed new discs?
