なきゃ from 行かなきゃ is an abbreviation of なければ
This is absolutely correct.
it would translate to "Must go"
This is not wrong, but not necessarily correct in this context.
行かなければ / 行かなきゃ
The literal translation is, "If I don't go...". That's it. With a couple of words attached the following may happen:
- "行かなければいい" (Don't need to go)
- "行かなければ宝くじが当たる" (Win the lottery if I don't go)
- "行かなければ結婚して幸せになれる" (Marry and live a happy life if I don't go)
What about now? Do you really have to go? I'd rather stay.
But as you mentioned, if you just say "行かなければ…", which no one actually says in real life excepts for emo kids, this implicitly is equivalent to "行かなければならない". This would mean "If I don't go, (it) won't work" = "I shall/must go".
But in your case, the consequence of not going is "not being able to know":
行かなければ (if one doesn't go)
分かる訳ない (there's no way one will know)
Notice it never says one must go.
With the above in mind, translate as follows:
- 領にでも + 行かなきゃ + 分かる訳ない
- To the 領 + if one doesn't go + (there's) no way to know
Shuffle them around:
- There's no way to know (what is happening) if one doesn't go to the 領
Which matches your translation:
- You'd have to go to the territory to find out (what is happening)
でも means "But"
Again, you are not wrong, but not correct here as it's "〜にでも". Check out this post for the usage: "事故にでもあったのではあるまいか。" grammar help please? [duplicate] . It's tagged as a duplicate but I think this is the better match for your case.