That would be fine as long as the fermenter can handle some pressure. It might even improve your beer. But if you're traveling a relief valve is pretty much required (like a cornelius keg).
Beer that appears to not be 'active' is still generating some CO2 - before the yeast are completely dead (which will take several months) they consume stored glycogen, and the last traces of sugar in the beer. Ever open a year old home brew? Mine are almost always highly carbonated by then.
In the secondary, the pressure should not be much, may or may not more than serving pressure. Primary, however, will reach undesirable pressures very quickly. Relief valve required for sure if you have more than a few points of gravity remaining.
