Milwaukee County's precariously balanced $1.4 billion 2010 budget could fall apart within a few months, forcing hundreds of additional layoffs, program cuts or both.The budget counts on more than $20 million in employee givebacks never approved by unions that represent 85% of the more than 5,000 county workers. Though County Executive Scott Walker initiated the giveback demands with his budget proposal, the County Board bought into a modified version of the plan.The concessions were a key part of the new budget's effort to plug an $80 million budget hole and include12 unpaid furlough days and trims to pension and health benefits. Enforcing those provisions could be another matter.