I was going to comment in your other thread about your MOV choice.
Thermally protected MOVs prevent fires caused by overly abundant MOVs that often don't offer much protection in the first place. A product 'dying' isn't as bad as one that goes up in flames and burns down the house. A TMOV that disconnects itself simply leaves that device unprotected to be damaged by the next transient instead of shorting and burning. Until someone invents a replaceable module that also disconnects the device upon failure, MOVs will be a limited solution to transient protection.
The best way for a device to be protected against an overvoltage transient is for it to simply withstand it without resorting to shunt absorption methods. Then you can back that up with a MOV or TVS that shunts extreme transients. In the case of your device, the problem is the lack of space between the operating voltage (~325pk and the inherent withstand voltage (the 450VDC rating of the capacitor, among other things). Your selected 385VAC rated TMOV will allow transients way above 450V before it clamps. A lower voltage MOV that would clamp at 450V would leak too much at normal operating voltages. Here in the US, if you want to make a transient-robust non-PFC SMPS, you use a 400VDC capacitor and a 170VDC bus voltage. You can find a MOV that fits between those.
A TMOV is a good, safe choice--but don't' worry about its lifetime. It is a sacrificial protection device and its life will depend on how much abuse it is subject to. When it has had enough, it will simply no longer offer protection. Just make sure that it actually offers protection--IOW, your device won't be damaged before it clamps. It would be pointless to have the TMOV clamp after the capacitor explodes.