If there had been a full stop/period (or maybe even a semicolon) between the two clauses (and if I had been familiar with the word [and this applies to most of the others used below] prior to reading your links!), I might have attributed the fact that “Je serais si heureux” is not repeated in the second clause to “l’asyndète” (‘suppression des liens logiques et des conjonctions dans une phrase’ under ‘Figures de transformation non identique par effacement ou suppression’ of link 1).
The clauses being separated only by a comma, however, I see the omission of the second “Je serais si heureux” more in line with “l’ellipse [Rhétorique]” (‘omettre un ou plusieurs éléments en principe nécessaires à la compréhension du texte, pour produire un effet de raccourci’, right below “l’asyndète” on link 1’s list), and even more so with “le zeugma [syntaxique]” (four entries below “l’ellipse”), which also involves avoiding the repetition of a common element, but not at the expense, as with “l’ellipse [Rhétorique],” of omitting an element that’s generally necessary to understand the text.
However, all of the above is probably rendered moot in light of my interpretation of the meaning of the sentence and its two propositions, because I feel that the author is actually saying the same thing in both clauses, which would make it more logical to choose from among “Figures de transformation identique” than from those (like the above) that are “non identique.”
With my interpretation (and non-literal translation) of both clauses (and therefore the entire sentence) being ... :
“Trust me, I shall return, but for now please leave me to my
silence,”
... I’d argue that, both clauses being “identical,” this style reassembles “l’expolition” (under ‘Figures de transformation identique/Répétition morpho-syntaxique’ in link 1) in that it repeats the same ‘argument’ in different ways;
and finally, to the (very limited) extent that two of something is enough to qualify as an accumulation, “l’accumulation” (also under ‘Figures de transformation identique/Répétition morpho-syntaxique’, about a dozen entries above “l’expolition”) could also describe this style.