They (the label) have nothing to do with your publishing (unless ur Mike Caren or LA Reid
).
As far as getting ur masters, more than likely, NO. Unless you have enough leverage where ur big enough to demand that then no.
Masters are one of the main component to a label. That's initially what their investment (advance) is in. They will try their hardest to retain the masters. Back in the day, before these 360 deals, the labels where spending millions marketing and building the brands of these artist. When the labels build them up big enough and an artist chooses to leave, they (labels) have to retain something.