The construction you are referring to in your first example is called passive infinitive which is often used in notices and instructions like:
The exercise is to be done three times a day.
This key is to be returned within 24 hours.
The phrase never to be heard of again which also contains a passive infinitive is used when something or someone seems to have vanished forever. Your other two sentences might be grammatically correct but they do sound a little awkward and there are probably ways to express the same ideas more clearly.
I hope I could help a little, take care!