For a tune, you would likely be on your own. You could ask them to prove it was something the tune caused to fail by exerting more power or force than the part was built to handle. But at that point you'll probably need to lawyer up.
For the 2985430985732985760432524348468436523846504325484784325043508435843515804519375984375843150984358431543150843586431585095098143798431755098436865984315094375984317509824375984360984359813759874350987435986431814356043156094315894315894365094316598346098561984356435098164350981435098437598432598432658431509843509843159843164309856431985698431659843165984375098432651984365983174098321893214083214983215891598150983215893217598321659843165098312983219853219843219853298434574643198532165321843219874098321432185321098659832155984316508321650984316509843165437509816509832750984325087587454343108985983256149315984315987431289704319856509843175098321083264098321749832109853210698431573219560983247932156983215687435687435987435698743165032145832165087143650874365753265874321431438587431587436509843158314509813259859832098743218569874315987435700843187732109832198329853210851320875139843509843198543198543109854319856087431508743187904321084319843109809887318763210898439009884510983256932159832175093214503298532106532984th time, tuning your car doesn't automatically void your warranty. It depends on what broke.
Also, people who have been tuned generally seem to idiotically make it known by being asshats and usually slipping up with their dealer saying "well.... I'm tuned, I better not get my warranty denied!" or mentioning it in caution and discretion as if they have something to hide. That + being a dick about it usually = Go fvck yourself. And I don't blame the dealership one bit.