This ~う/よう is the volitional form, but the actual meaning is presumptive, as in 雨が降ろうと槍が降ろうと or 何があろうと. This is from a classical usage of ~う/よう, which is equivalent to ~だろう in modern Japanese. When the verb is non-volitional, all the volitional forms are presumptive (雨が降ろう can't express the rain's will to fall, right?), but as for volitional verbs, you need to interpret the meaning from the context. 受ける can be both volitional and non-volitional, but it's non-volitional in your example since the meaning is "to experience/encounter".
Yes, this makes sense. Although until today I had thought of 雨が降ろうと槍が降ろうと and 何があろうと as too different categories of expression ('whether or not' and 'not matter') but on examination of the link bentenmusume-san gave and from your comments it's clear that these are very similar things in Japanese, it's just that the English that expresses them differently.
Also, you need to realize that どんな is necessary only for "no matter if", and it's not for "even if".
I meant, 「多少バランス崩壊を受けようと」 = "Even if (she) experiences a certain amount of instability, ...",
parallel in grammar to「どんなバランス崩壊を受けようと」 = "No matter how much instability (she) experiences, ...".
Actually I guess on reflection that's "No matter -what kind- of instability she experiences. I should be saying,
「どんなにバランス崩壊を受けようと」for the meaning I was trying to compare to.
I think that's what you mean by the difference of "no matter if" and "even if" ?
It's 多少険悪なバランス崩壊を受けようと, not 多少バランス崩壊. 多少 modifies 険悪な or 受けよう (both interpretations are possible), not バランス崩壊.
I left 険悪な out as extra description of 受けよう that doesn't affect the underlying grammar point, but modifies the meaning of the sentence in a straightforward adverbial way....
But if 多少 can be modifying 険悪な rather than modifying 受けよう, then my other point maybe isn't illustrative of anything.
If 多少 can modify 険悪, then you don't need either a quantifier (e.g. どんなに物理が得意だろうと、試験のときは油断してはならない) or a
list of alternatives (e.g. 雨が降ろうと雪が降ろうと明日のパーティーには必ず行くよ)...
While the meaning would be different, you could be correct in saying simply「バランス崩壊を受けようと」, or something like 「りんごを売ろうと、買わない」
This puzzles me because I don't think I've seen a sentence using this conditional ようと that wasn't preceded either by a quantifier (usually an extreme one), or a list of alternatives (usually expressing extremes by example, or else expressing 'whether or not' type opposite alternatives), and all the examples at the link bentenmusume-san provided fall into one of those categories.
But, that's perhaps just what is most common, not the only thing you can do?