I certainly hope the pilots were on the correct frequency but if they had tuned the VOR instead of the ILS, and then decided to changed to a LOC-only instead of an ILS approach when they couldn't get a G/S signal, that should have set off alarm bells in their heads. I can only say that if it happened in future to any of us flying IMC, we should not hesitate to initiate a go-around immediately.
It still does not explain why they might have ignored an anomaly on the ADF if the NDB was tuned. The frequencies tuned will be the most important aspect in resolving this most puzzling accident. I do hope the preliminary investigation report will be released soon.