1st....Adding a chip will not automatically void a warranty, the proof lies with the repair facility to prove any fault lies with the add on product.
2nd...it will not reduce mileage.
3rd...it will most likely not reduce the longevity of mechanical parts, unless you are prone to hot rod your truck.
My MP-8 was added to my '05 Dodge 170K miles ago, no mechanical issues yet.
My mileage increased..albeit small, but even at a minimum 1 MPG increase over the 170K miles, the $500 cost has paid for itself 3 or 4 times over. The additional torque and HP increases do come in handy as well.
Regards
Gemstone