Create a new master project with each of your projects as subprojects.
Expand each of the subprojects, select dependent tasks, and link them with
the appropriate dependencies. Close the master project without saving it,
but when prompted, save the changes to all of the subprojects. This process
will set the cross-project dependencies correctly.
As far as the people issues involved with using cross-project dependencies,
you will probably face the same problems you faced previously (as you
stated, "...PMs "accidentally" deleteing links, forgetting to accept
changes, etc. and this has caused a lot of chaos for the PMO to manage the
plans on an ongoing basis). Therefore, you will need to make this a
training and performance issue with your PM's. Hope this helps.
Dale A. Howard [MVP]
Enterprise Project Trainer/Consultant
"We wrote the book on Project Server"