According to a previous ticket (QTIFW-1936), the maintenancetool exits early as it is running a batch tool to allow removing the actual maintenance executable during uninstall.

This means that if run with installer.execute, execution won't wait until it's done. The proposed solution is to 'delay' and repeatedly check for the directory to be deleted (see linked ticket for code sample). 

However, how is this delay supposed to be achieved exactly? Considering neither setTimeout/setInterval nor await/async are currently available in the scripting API.