~고서라도 == -고서 + 라도 == -고 + 서 + 라도.
Detailed explanation of this phrase can get complicated, but since your Korean comprehension level seems pretty high, I'll go through it and give you a taste of advanced verb endings.
-고서라도 involves three connective components. It might look unusual but it's actually a fairly common form.
* -고: expresses two actions in sequence (숙제하고 자다), or two concurrent states (검고 푸르다).
* -서: coming after -고, -(아/어), -에, etc. sharpens the first verb's meaning. For example, -고서 is a stronger "(something happens) and then ..." than -고.
* -라도: after a verb, adds the sense of "even if it means (doing something undesirable)", "even if it is by doing ...", "even if it necessitates ... ", etc. There is also -더라도 which is similar but attaches directly to the verb stem.
Given the variations in each of the three components, there can be several different expressions of this kind: -더라도, -고서라도, -(아/어)서라도, etc.
Here are examples using 빚지다(take a loan), which conjugates to 빚지어 (빚져), and 빚지고.
Their meanings are given in English while trying to differentiate them as much as possible.
For practical translation, we can just use "even if it meant ..." for most cases.
1. 빚져(서) 집을 사겠다 (I will buy a house by taking a loan): -(아/어) + optional 서.
2. 빚지고(서) ... (... after taking a loan): -고 + optional 서.
3. 빚지며 (taking a loan): -며. (-며서 doesn't exist)
4. 빚지면서 (same as #3): -면서 (-면서 and -며 are about the same)
5. 빚져(서)라도 (even if it is by taking a loan): -(아/어) + (서) + 라도.
6. 빚지고(서)라도 (even if it is after taking a loan): -고 + (서) + 라도.
7. 빚지며라도 (even if it means taking a loan): -며 + 라도.
8. 빚지면서라도 (same as #7): -면서 + 라도.
9. 빚지더라도 (even if I take a loan): -더라도 directly after the verb.
10. 빚져야(만) 하더라도 (even if I have no choice but to take a loan): -져야(만) 하더라도 (even if I have to ...)
11. 빚진다(고) 하더라도 (even if it meant I'd have to take a loan): similar to -져야 하더라도, with a subjunctive feel.
Most of these expressions are natural and are actually used.
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