Subjunctives in Chinese
I disagree with the translation into English of this use of the subjunctive. 

The structure
May + [SUBJECT] + [VERB in infinitive form] in English generally implies a type of volitive subjunctive in the Romance languages, where 
the speaker has the authority to wish (or even to will) that something happen. 

Here though, I would see the original language construction is as a potential subjunctive, which in English would have [SUBJECT] + may + [VERB in infinitive form], which would result in:


  The infinite may become starless


In this case, though could precede the subject and introduce the condition.


  Though the infinite may become starless


If there is a hint of any volitive or optative subjunctive however, we could replace though with the construction rather that before the subject, and keep the subjunctive:


  Rather that the infinite become starless




In Chinese, which lacks the distinction of indicative, subjunctive and imperative moods in its verbs, additional indicators of the grammatical mood are required. But they need not be attached to each verb that has the subjunctive in Spanish or to each occurrence of the word may in English.

If we establish that this is a potential subjunctive, then the use 可 as a monosyllabic verb before the main verb is an adequate literary device; depending on the rhythm, we may want use the diysllabic 可以 or 可能 which is a little more common in daily speech and thus a little less elevated. 


  无穷苍昊可逝星
  
  无穷的穹苍里的星星可能消逝


I've translated the other vocabulary items differently depending on the style, and have translated become starless with an equivalent of lose stars or the stars disappear .

Using 虽 or 虽然 in the first clause can reinforce this sense of potentiality if necessary.


  虽无穷苍昊逝星 / 虽无尽天可逝星
  
  虽然无穷的穹苍里的星星可能消逝


But if we do want to add a sense of the emotional dependency, much as English can add Rather that instead of Though at the beginning before the subject, the disyllabic word 宁愿 can begin the sentence, or the similar 宁 (in an elevated classically-influenced style) or 宁可 (in more common speech) can precede the main verb; these are often followed by 也 with a negative verb or a verb of regret or non-volition in the volitional clause (like in Italian and Spanish, but different to English's main clause with than after a clause beginning rather that). Such mutually dependent clauses are often a characteristic of Chinese sentences. 


  宁愿无穷苍逝星 / 无穷苍昊宁逝星 ...
  
  也惜你瞳乌死去 / 但愿你瞳也不亡
  
  
  
  宁愿无穷的穹苍里的星星消逝 / 无穷的穹苍里的星星宁可消逝 ...
  
  也愿你眼孔乌黑不至面对死亡 / 你眼中瞳仁的黑孔也不要死去


I hope that gives you a few more tools to use in your translation.