Complete sentence: Is the subjunctive mood suitable for this case?

The worst that can happen is that he fail/fails/would fail/will fail the exam.

Which of these is (or are) correct? In Spanish, the subjunctive mood would be used, is the case similar in English?

Solution 1:

The worst that can happen is that he fail/fails/would fail/will fail the exam.

The subjunctive fail sounds a bit off to me here. As a subjunctive clause, that he fail the exam is flawless, but in English, the subjunctive is most often used to convey a request or command: She insisted that he give that student the failing grade he deserved. (The subjunctive is also used in a few other cases, none of which apply here.)

The declarative fails and will fail strike me as acceptable but informal. Would fail is all right. Should fail/can fail/could fail are all acceptable too. Should fail is a bit formal.

Solution 2:

"fails" is correct. The sentence then means that the exam is in the future and he might fail.

"fail" is wrong in this instance since the subject is singular, and fail would be used for a plural subject.

"would fail" can not be used in this case. It would be used in a situation like: He didn't want to try because he thought he would fail.

"will fail" I am unsure about. But I think it comes down to "tense simplification" Michael Swan's Practical English Usage:

If the main verb of a sentence makes it clear what kind of time the speaker is talking about, it is not always necessary for the same time to be indicated again in subordinate clauses. ... And: Verbs in subordinate clauses are often simpler in form than verbs in main clauses - for example present instead of future, simple past instead of would + infinitive, simple past instead of past perfect. You'll find Coca-Cola wherever you go. NOT: wherever you will go.