The Mexican trio Belanova use the haber + de + infinitive construction repeatedly in the chorus of Por Ti:
Si mi vida ha de continuar
"If my life should continue"
Si otro día llegará
"If another day will come"
Si he de volver a comenzar
"If I should start all over again"
será por ti.
it will be for you.
[Captions 6-9, Belanova > Por ti]
As it turns out, the haber+de+infinitive construction, often found in music and literature, is deceivingly difficult to translate with precision. A native speaker staff member tells us that, in the context of this song, she gets the sense that ha de continuar expresses possibility ("if my life is to continue / is going to continue") more than obligation ("if my life must continue"). However, generally speaking, haber+de+infinitive, does convey a sense of obligation or necessity, though often milder than the tener+que+infinitive construction ( tiene que continuar -`"has to continue") or hay que+infinitive construction (hay que continuar -"has to / must continue").
For this reason, in the end, we chose to use "should" in our English translations as it is nicely ambigious, conveying a sense of possibility but also having the alternate meaning of mild obligation.
Note that haber+de+infinitive and hay [also from the verb haber] + que + infinitive are completely distinct, and used in distinct contexts. So, how should you decide de vs que? You see, hay que continuar, loosely translated as "one has to continue," would always express a generalization. Meanwhile, the first-, second- and third-person conjugations of haber -- that is, he, hemos, has, han, ha and han -- plus 'de' yields a more specific, though milder sense of obligation, or of possibility, as in our featured song.
A final note regarding the verbs in Belanova's provocative refrain: 'Volver a comenzar' could be translated bit by bit as "to return ['volver'] to begin [comenzar]." But in English, we tend to say "to start again" or, with more emphasis, "to start all over again."