Where would Iceo flow through and would it cause thermal runaway?
R2 doesn't really do anything with thermal runaway. The voltage divider network of R1 and R2 make the voltage bias for the base to emitter junction. When Re is added to the transistor circuit, it controls the base to emitter current to DC ground. Without this, the only current limiting it has is its intrinsic resistance of the junction that defines BetaDC.  When the transistor heats up, this resistance goes down, and the betaDC goes up. So it takes a smaller amount of base current to make more current flow in the collector. Putting a current limiting device in the emitter circuit will limit the base to emitter current, and this action prevents thermal runaway. It also (emitter resistor) presents a load for the base to emitter junction so the incoming signal doesn't present an overload condition in the base to emitter junction.

Those papers like that rarely gives you good circuit explanations.