If you apply the patch from that link it will cause the BB to not delete any old appointments from outlook. If you want it to delete them off the handheld after XX days, you can configure that in the sync properties of the Desktop Manager.
In it's original configuration, my BB tried to delete ALL my appointments from outlook - not just those older than 90 days like the support site suggests. I use it to record time for monthly billing so this was muy no bueno!
You could always backup your calendar to a .pst and then see what the BB does if you let it have its way