I don't need to know every detail, just that one. If Jesse isn't smart with his boatload of cash, it will get him in trouble. If Jesse gets in trouble, he becomes a liability to Walt. So yes, it IS necessary to Walt's scheme that Jesse has a plan of some kind. Jesse knows enough shit about Walt to bury him for LIFE if he gets busted and then offered a plea bargain. Whether he would take it or not is irrelevant. Walt wouldn't leave a huge loose end like that if it came up. As for the DEA, they aren't interested in Jesse right NOW but if he got busted by the IRS for having way, way more money than he should, you can bet they'd become interested again. Small-time dealers don't make the kind of scratch Jesse has.