TN Status - changing employer while living in USA

1. Suppose a person (Canadian) works on valid TN status and therefore lives in USA at this time. He wants to change employer and goes to the border to apply for a new TN. Would it be a problem that he currently does not have address in Canada and therefoe may be considered as not maintaining residential ties in Canada?

2. What would happen to his current TN visa (which is still valid for a long time) if a new TN visa is denied?

Your help on this subject would be higly appreciated.

1. One doesn't require foreign address to enter on TN, nor maintenance of foreign ties. You live in US, quite legally, on TN. TN is not a tourist status.
2. Nothing. In fact, even if approved, your 1st TN is still valid, since you should still keep it for a couple of weeks (while you give notice, etc). You don;'t quit your first TN job until yoursecond one is secured.