hello,
using your data the thermal resistance of your microstrip transmission line is about 1.1K/W, which implies that when handling 30W the temperature increase will be about 30K. If you are working at normal temperature (eg 20degC) that means that the transmission line will reach about 50degC at the input (and approximately 70degC at the output lines if you combine two 30W signals). In principle, duroid withstands more than 150degC, so the transmission line will not impose a problem to your design.
I was assuming substrate thickness 31mil=0.78mm, 50ohm width is 96mil = 2.45mm; epsilon=2.2; TRL loss=3dB/m. However in the first post you mention that 70ohm line = 15mil, which gives to me a thickness of 10mil for the substrate, and about 6db/m for the line, which turns to give about 4K/W for the thermal resistance of the line. assuming 30W this means a temperature increase of 117degC for the line, which is very close to the 150degC limit at the input, and above it at the output assuming 50W !!.
other thing is the loss of the power combiner. Bear in mind that the loss of the combiner translates directly into heat, so you should consider that problem carefully.
furthermore, one other thing is the power handling of the resistors of the design. when both input signals are present, the resistor does not have to handle power, but when only one signal is present, one half its power is routed to the resistor, so be careful!
rgdz