Good question, and I agree the key variable is the resulting blade angle. To put the bottom line on top I believe you will get more thrust.
As stated the Tq and RPM are fixed hence blade drag and rotational airlfow are fixed. And the question is how does thrust vary as a function of rho?
For a given blade drag (ie Tq) and RPM (rotational airflow) the Cd of the blade must reduce as rho increases. Therefore the blade angle must also reduce but does that result in more or less thrust? The answer depends but if we assume that 80% Tq puts the blade at a higher angle of attack than its most efficient the answer is the thrust will increase: because under that assumption the slope of the Cd curve is steeper than the Cl curve, and/or the total reaction of the blade is more aligned with the thrust axis as the blade angle reduces. I think.