I don't shop at Wal Mart, and this is one of many reasons why. The business model of selling cheap things at super cheap prices only works because the rest of us (tax payers) end up picking up the part of the bill through heath care costs, at least here in the US.
But Wal Mart is not evil, they are simply doing what all businesses do, attempting to make a profit by whatever legal means possible, and they couldn't do it without the cooperation of their customers, employees and the government. If people stopped buying from Wal-Mart because they don't pay a living wage, War Mart would raise the wages. It wouldn't even add the much to their overhead, Costco manages to pay their employees a decent wage while still offering low prices, so it can be done.
As far as employees, it's not as simple as just getting a job elsewhere, it's a tight economy and there aren't a lot of jobs out there for lesser qualified workers, but if every Wal Mart employee made the effort to make themselves more employable through education and training, many of them could probably get better jobs. If enough employees did that it would force Wal Mart to compete.
And if the government required employees like Wal-Mart to cover health care costs for all employees it would level the playing field for businesses that do the right thing by offering it. They also need to do something about illegal immigration, which helps keep wages at a lower level.