[X] Accept this humiliation [-1 Treasury, -.1 Income, -1 Influence, -3 Prestige]
Either we aren't hurt that badly and we can still repay or we are hurt that badly and in that case, we would be weak enough for them to extract payment by force.
You can't extract payment by force if there isn't anything with which to pay: if the Khem take everything, if the Ymaryn are run dry (or who knows, collapse for a second time).
Extracting payment through force is also made more dubious by the bottleneck of Trelli, which exists regardless of Ymaryn absolute "hurt". What are they going to do, blockade everyone else from going there?
Berba or any other nation with an inch of sense (aka all of them) isn't going to loan out that much money
Maybe, maybe not. Speculative fever can lead to taking on of many more risks than originally intended, if they see this as funding the increasingly inevitable takeover of the Ymaryn's old provinces (and miss the Khem threat).
Worse, if they already have an economic incentive, in the form of previous loans, they're all the less likely to consider the failure case. "It is difficult to get a man to understand something, when his salary depends on his not understanding it", and all that.
Of course, if they do notice the Khem rationale, I think you're right. (Or if they have sane risk management, which is always possible, but never a sure thing with humans.)
When we lent money to Amber Road, there was no talk about going to war with Norsca to ensure that they would win and be able to repay us. In fact, the idea never came up at all by either anyone in the thread or any character in-universe.
We would have totally sent troops to Amber Road, just not because of the loan (which we're inclined to forgive anyway). Actual friendship--or, for the cynical, long-term strategic interest--is a far stronger motivator than economic ties. Economic ties are just an additional incentive: in Berba/Abyss' case, in addition to the fact that they already, actually hate Khem from the wars.