"Convert to Editable Poly" equivalent for Maya, e.g.: destructively merge this with a cube and delete history, "baking" and "flattening" the shape back down to a simple mesh.

flatten.py

import maya.cmds as mc

original_selection = mc.ls(sl=True)
mc.select(mc.polyCube(ch=1,o=1,w=1,h=1,d=1,cuv=4), r=True)
mc.select(original_selection, add=True)
merged_shapes = mc.polyUnite(ch=1, mergeUVSets=1)
mc.select("%s.f[0:5]" % merged_shapes[0])
mc.delete()
mc.select(merged_shapes[0], r=True)
mc.delete(ch=True)
mc.delete(original_selection[0])
mc.rename(merged_shapes[0], original_selection[0])