The script to install WordPress is available in the GPL as well as the PRO version of Virtualmin. This is via Virtualmin → Install Scripts
I am not sure what you mean by ‘script to be able to re-install WordPress’. Is there a re-install script in the PRO version of virtualmin which is not available in the GPL version?
You are right, of course, to think of those who will come after you and take over the project. To that end, virtualmin GPL offers the option to upgrade WordPress from an old version to a new one, as and when a new version is released. This too is done via Virtualmin → Install Scripts. Is that what you meant by re-install?
If so, be assured that your successor will be able to keep WordPress updated merely by going to Virtualmin → Install Script and electing to upgrade, even with the GPL version of Virtualmin.