Kevin,
I would go much higher. More like 98%.
The car example is perfect. If you do not replace the tires (IOW form a new gov't?), the tires will eventually wear out & fail.
There is the push and the pull. The push is the extra $1trillion/year in new debt (talk more about that later). The Pull is the $22.2 trillion current national debt, but if you add the local/state/future unavoidable debt, we're closer to $100 trillion. That level of debt is hard to imagine. All US mortgages are $10T, so this debt is 10x times all mortgages combined. It is about $300k per person (from newborn to 100 year olds).
The push is even worse. We start with a near-impossible debt level. But we're being worse than stupid & jacking it up every year. The extra $1 trillion is just the national debt, far more is added state/local plus long-term debt pensions.
There are only a few ways to address this. The 2% likelihood is if our gov't (and our people) get serious and stop spending and start attacking this debt. Possible? yes. 2% possible. The other scenarios make up the 98%. Economic collapse. Massive devaluation of the dollar (slow or fast). Gov't failure/takeover (revolution?). Currency replacement (basically devaluation). Other forms of major War. You may consider some of those as better than others. But 98% it will end badly.