Decal is generally formalin + decal solution. If it was pure decal without formalin then the specimen would probably be ruined after 3 days. IF you're worried call employee health. I'm sure they've encountered it before.
From what I've seen on the containers at work, our decal doesn't contain any fixative. It's just a mixture of acids. Generally, if you want to leave something in decal for an extended period, make sure it's well fixed 1st or use a 50/50 solution of decal & formalin.
PS: Were your slides really pink when you looked at them?