This wouldn't be a very historical implementation of dept at all in that case.
Some historical examples:
- UK paid back their WW1 dept
100 years after, and there has been similar news recently for their WW2 depts ( 70 years after ).
- War bonds took many decades to pay back with many in USA being paid back in the 70s.
If it's the act of being in debt that's important to you then it is infact already in the game in terms of the US warbonds NF that reduce consumer goods by -5% ( and other similar NFs )
In a total war like WW2 money can't magically buy you a tank. What matters if you have access to the resources, the factories and the labor to make that tank, and if your workers are motivated enough to work overtime to make more of them. The only part of the economy that matters in total war is how much of it that needs to be dedicated to civilian matters and how much can be diverted to the war effort which is perfectly modeled by the Consumer Goods ratio.
So you think that Switzerland would have been able to make an attack costly because they planned to resist?
Let me tell you a secret... ALL other nations attacked by Germany in 1939-1941 also planned to resist, in equal amounts that Switzerland did, and it did not go very well for any of them except for the one that had a war economy of similar size, an army with modern weapons of similar size, plenty of land to trade, millions of soldiers to sacrifice and immense external support to rely on. Not one of the other nations made it costly for Germany to take them. Not even France, universally agreed to be the most powerful military power before the outbreak of WW2, could offer serious resistance.
Switzerland had zero external support, was a very small country of 4.2 million, had almost no modern equipment (tanks/planes) and were surrounded by Axis on all sides of them. Germany had access to paratroopers & mountaineers with experience from the Norwegian campaign as well as an airforce several 100 times stronger. Something else that can't be overlooked is that all branches of the German forces knew they were unbeatable after just having knocked over France like a walk in the park, while the Swiss soldiers knew the Germans were undefeated and unstoppable, and that they could count on no help from anyone, so their situation was truly hopeless.
I would be surprised if Italy and Germany would have needed more then a week to secure Switzerland if they attacked them right after France.