The best way to test this (I’m a pclay artist as well:) is to cut off a very small piece of a toobie. Set it on a piece of plain white paper on a tile and put in a preheated oven at 285 degrees for 30 minutes. See how it holds up. If it melts or distorts – well, then you haven’t ruined your mixed media piece OR a whole toobie! You could actually wrap a small amount of clay around the toobie bit before baking to even further replicate what your end goal is.
Let us know how it works out!!