Alecia, afternoon..... I think the bad stuff in chicken would carry over and contaminate the next food group..... I have heard of folks using an acidic marinade for pork and then cooking it down for a sauce.... using a high temp for the reduction to kill stuff... Of course the marinade was refered the entire time... and reduced for that pork meal....
Holding a milk based sauce over time scares me, but then I don't know squat about it...... I wouldn't do it unless a food expert lined out the critical elements to it's saving, and it's specific uses....
Maybe if you heated it in a double boiler to 185 for an hour or two immediately after removing the chicken, to pasteurize it, MAYBE it would be safe....
Second thoughts...... Send me your e-mail and I will pay-pal you the cost of a new quart of buttermilk..... I'd lose sleep at night if you weren't here to post your recipes and Q-Views....