I have recently installed PyQt4. The installation was successful. Is it good practice to now delete the PyQt4-4.11.4-cp37-cp37m-win_amd64.whl file? Will this prevent me from using pip uninstall PyQt4in the future?
You could delete the wheel package. It won't prevent you from uninstalling the package. 
If, however, you need to reinstall the same package again, you will have to acquire the wheel package again, obviously.
Should I delete .whl installers after packages have successfully been installed?