Why would they be unemployed? It's hard to make the argument that McDonald's (and similar) would make cuts to its work force if the minimum wage were higher, considering their profits are already ridiculously healthy.
McDonalds has about about 1.7 Million employee's. For arguments sake lets round that down 10 1.5 Million. Assume none of them work full time, in-fact lets say they work 1/3 of a full time job so about 700 hours a year. That's just over 1 Billion labor hours a year. Now they make about 5 Billion in profit so just how much more pay can they squeeze out of that? Every dollar increase in base pay would shrink profits by 20%.