Extending a PTC voltage rating with series resistance
Most likely, if you provided a lot more information about what you are trying to do, a better way could be proposed. I really think that using a PTC for over-voltage probably a mistake. But, considering that the normal working voltage is only 4V (based on your comment) and that you are targeting a 20V cut-out, I think this has a chance of working.

One way to look at it is this. As the PTC starts to trip, its resistance will increase in a short time from some low value to some high value. We don't know exactly how fast this process is, but we can be sure of one thing. The maximum power dissipation in the PTC will occur when Rptc = Rload.

Since the load is 22 Ohms, the highest PTC dissipation will occur at that instant when the PTC's resistance is 22 Ohms. At that moment, the voltage across the PTC will be half of Vin. So that is 20V across the PTC in the worst case. That is actually fairly promising, because it is lower than the maximum allowable voltage. Also, the current will be roughly 0.9A at that point. So the instantaneous dissipation will be 18W (V * I). Now, prior to this instant, current may be higher, but the voltage will be lower. And after this instant, the voltage may be higher, but the current will be lower.

I can't guarantee anything, but it seems to me that 0.9A is pretty reasonable, and 20V is below the maximum allowable voltage. So I believe that the PTC will survive this.

I have not tried to validate your basic scheme. I didn't do any calculations with Itrip and Ihold. The cutoff of this circuit will definitely vary from unit-to-unit and also over temperature.

I also want to point out that the normal use of fuses is to make sure over-current events don't overload conductors and start a fire. The PTC you have selected may not provide reliable protection for faults other than over-voltage input. For example, if the output is shorted. In that case, unlike your proposed scenario, the current will not be limited by the load resistor, and the PTC may be permanently damage.