To take this further... To mean anything, this guarantee needs to apply unconditionally and forever. Even in 50 years... Even when the manufacturer is bankrupt.

To do that, There could be a "Will Work Guarantee" organisation. The organisation will administer refunds to all customers with claims, (and combat fraud). Companies who want to be members of the scheme must pay into the scheme to cover payouts for their own products, plus a deposit for future failures of their products if they go bankrupt.