Anytime you switch systems you lose the legacy parametrics (unless you buy a seat of Elysium which is around 60K).  I have a client that switched from Pro to Inventor...all 500 of their corporate licenses.

There is always a lot of factors that go into a switch, the biggest one is usually renewable cost which Inventor and AutoCAD combined are less that a ProE renewal.

Really there are too many questions to ask to pinpoint the success of this endeavor but the first one is...

How much legacy work needs to be remodeled and how often?  Are you okay with just reusing a part and when a retool needs done to recreate it from scratch?  The answer to this can lead us down many paths, but Fusion is usually involved in most of them.  Fusion will allow you to edit the solid in a very dynamic way without the original parametrics.

In the end, this may be a great question for your reseller.  I have seen too many companies try to switch without consultation and training on the new software.  I don't care how good you are in ProE you can always benefit from even an Intro Inventor class or a custom class with Intro and Advanced topics.

I worked for a company that switched from UGII to Wildfire. One of the criteria was that we had to train our designers for Wildfire. Each designer had 12 days of training and some had an additional 5, depending on their job function.

We were lucky that we made the decision to keep existing products in UG and only design new products in Wildfire. A few years later, that division got sold off and the ebgineers had to go through training again as the new parent used CATIA as thei corporate standard.
 

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli