Yes, it is possible to revert back to V2 after updating to V3. However, once you are out of Mapbox or Nearmap credits in V2, you will no longer be able to access the imagery import feature since these two types of credits are no longer available for purchase.
If you need to re-download V2, you can get it here.
To re-install v2, just install the RBZ using the SketchUp Extension Manager and then be sure to close all SketchUp windows before restarting.
You may need to reactivate your license after downgrading.