No, you won't see any fluctuation with the sensor disconnected because that disables the entire lambda system.

If you disconnect the O2 sensor the system will run on the basic mechanical mixture only, which should be slightly rich, so the sensor voltage will be constant and high.

It's best to leave the O2 sensor in the circuit by pulling the connector just enough to attach a small test lead to the exposed pin. Now you have a parallel connection and the circuit is undisturbed. With a scope you should see the sensor voltage jump back and forth between about 0.15 and 0.85, and you can evaluate its response time. It should complete about one to three cycles per second at idle. With a voltmeter it should read the average output which is about 0.45 volt.

The first rule of testing an operating circuit is that the test set up CANNOT effect circuit function or your results are garbage.

Duke