Like in my previous posts, I had the excatly the described problem with iPad mini. I carried he iPad Mini (14 months old, warranty expired after 12 months) back to point of sales where I bought it. I have had a discussion with Apple care Finland reps about the problem - guidance beining "if you think that the product is not working like it should you can claim according to EU consumer laws a working product". I acted based on that guidance. Device got sent to repair. I got a new replacement device which is now working without any problems.
And I have also a pending email from "apple wireless" engineer - you have had a problem with WiFi connectivity, can you elaborate the details of environment and network setup...
To me this WiFi connectivity stops working with iPads/iPhones sounds like problem which is not solveable by consumers with means what we are having available. I got a replacement unit after expried warranty perioid without any charges. And if the issue would be solveable by myself or just with reset tricks the replacement would not haven't be done.
I'm really afraid that fellows outside EU or "kind of grey import" customers - there is no recovery for the issue with the means what we are having available, just referring the fact I got the replacement unit after the official warranty perioid has expired. If there would have been "reset" trick to recover, I would assume the service point have done it for my iPad and charged some fees from me.
For EU area victims. use the "EU consumer law statement of working product like expect". That last's 24 months despite of manufacturer 12 month warranty perioid.
Just as curiocity, I'm working on wireless device industry (you can make you your conclusions for which company). And based on that experience combined with warranty threatment, I assume that there is no magical trick what you can do to recover from WiFi not working issue. Something get's badly broken on WiFi and it can't be fixed with any reset's or WiFi box configurations.