So to uninstall Citrix you have to have the Citrix IMA service running properly. Which of course begs the question of what you do when you are trying to uninstall because the IMA service ISN’T working properly in the first case?
Open command prompt, navigate to the directory that has the Xenapp install MSI and use the command
msiexec /x mps.msi CTX_MF_FORCE_SUBSYSTEM_UNINSTALL=Yes
That will take care of the issue for you and force an uninstall