Do you mean within this line only, or in Helena's speech which precedes it?
If this line: what Helena means is that the way Hermia and the boys are mocking her (as she thinks) is partly her own fault (you may have noticed she tends to be a bit of a drama queen and likes to feel sorry for herself). She says this in the line before. The whole line is, 'Tis partly my own fault, which death or absence soon shall remedy'
In modern English she means: OK, it's partly my own fault for trusting you lot - never mind, I'm going to end this situation either by killing myself or by leaving (neither or which she has any intention of doing, by the way).
The devices would be:
- personification of 'death' and 'absence'. Personification is a form of metaphor. She is speaking as if death and/or absence are actually able to take an active part - 'remedy' the situation.
- you could also say hyperbole (exaggeration) is being used as she is making a huge issue of being teased (even if she were actually being teased it isn't enough to kill herself about)
- Then of course there is the iambic pentameter in which the line is written (five 'beats' or feet - daduh times five)
This "either/or" statement uses the literary device of juxtaposition. Helena juxtaposes, or puts together, the concepts of death and absence, by saying one or the other will happen to her soon. But Shakespeare, of course, being Shakespeare, uses juxtaposition in a larger sense for both comic and thematic effect. Helena is dead serious in this utterance. She is at the end of her rope, completely exasperated, when she makes what is also a hyperbolic, if heartfelt, pronouncement about her death or absence. (It's hyperbolic because clearly no one will die in this zany comedy, dark-tinged as it might at times be.) She believes the men, who to this point have had eyes only for Hermia, have ganged up on her to mock her. She condemns herself for allowing herself to be so vulnerable. But the men are "dead" serious too: the love potion means they really are besotted with love for Helena and willing to fight to the death for her. Helena's statement is thus part of the dramatic irony of this scene: the audience knows that Helena is not aware of the effect of the love potion on the men. We know the men are in love. Helena's statement and the groping for logic and reason it represents (after all, she is right: how could it make rational sense that both men have suddenly fallen in love with her?) is, therefore, in a large sense, juxtaposed against the theme of madness that the play argues love induces in people.
I meant this line only and how it ties along with Helena's speech.