4. Established inbound, you've leveled off at MDA, then NAVAID failure or suspect whilst inbound - Initiate a climb immediately to where you dead reckon the aid to be and conduct missed approach procedure?
Close but no. More correctly: Initiate a climb immediately and track to where you DR the Missed Approach Point to be. The MApchPt is not always at the aid, and we need to be careful about the mindset which assumes it will be.
Without my plates at hand, I can think of two where it isn't so: Mareeba VOR Approach and Cooktown NDB Approach. Once at the MDA, DR tracking to either of these aids after a failure could easily be fatal.