Johan and North's joking conversation about debt is cute and steeped in sweet earnestness.
I think when Johan answers "What if I said yes?" to North's question about them being in debt lets North know that Johan isn't actually in debt (along with the amount Johan says).
We've seen how North is when he is in debt! He may panic and complain but he also takes care of business. He got three jobs to pay off the debt (Johan just didn't like him working and thus...the "agreement" they have now) and was willing to wheedle and whine his way to a lower interest rate. While 1 billion baht is a lot different than what North had going on, I think North would still be willing to figure things out with Johan in a practical way.
Since North knows Johan isn't actually in that kind of debt, his immediate answer is to flee the country after quoting how much his organs are worth. (It would not surprise me if North actually did look up how much his organs were when he was first in debt to Johan. I just don't think it was a lasting thought before he just decided to work work work work work.)
And when North says he would find a job but they wouldn't have a lot of money and wouldn't be able to eat, Johan nods in mock solemnity. It's a really cute moment. Cherry on top is North asking Johan if he'll starve with him.
Out of all the scenes in Fourever You, it's my favorite in how it shows a domestic conversation between the two. It's a scene that really cements for me them being a couple.
