This construction is used to talk about things which are reasonably expected to happen, most often as the result of a decision. The first "be" verb refers to the expected possibility, the second refers to the expected state of being. This is very correct, very high-style English, but the grammar does not make logical sense. Let me explain how this happens.
English speakers do not like dative constructions and do not use them often. For example, if the room temperature is low, they will not say "To me it is cold." They will say "I am cold." The air in the room is cold, but they speak as if their own bodies were cold. This substitution is dictated by the aesthetic rules of English which greatly favor sentences with animate subjects.
The double-be construction is the result of such thinking. Let us start with a dative example:
To me it is to be your guide today.
Though this sentence is perfectly logical and perfectly grammatical, the native speaker will consider it ugly, if he understands it at all. He would say:
I am to be your guide today.
Here he has changed the grammatical subject of the first "to be" verb from the abstract circumstance "it" to the animate "I". Logic has suffered, but aesthetics have been improved.
When you posted the bounty you asked specifically about the difference between "if that was the basis" and "if that was to be the basis". Remember, the double-be construction indicates that something is reasonably expected to be. So, "if that was the basis" is talking about a fact which may or may not have take place in the past. In contrast, "if that was to be the basis" is talking about a reasonable expectation which may or may not have existed in the past. Consider these examples:
You say he was dismissed for theft. If that was the basis for dismissal, why did they not file a report with the police?
Was he dismissed for theft or for some other reason?
You say he was dismissed for smoking. If that was to be a basis for dismissal, why was this not mentioned in the rules of workplace conduct?
Did the employer give employees a reason to expect that they would be dismissed for smoking at work?