That is a hard question to answer. It shouldn’t ’wear down’ over time, but it is made with electronic components, so it should have the same sort of failure as your TV set, or smart phone , or computer ( close to zero, but not quite zero). It is, after all, a computer itself, with a CPU and RAM. 

There has been some discussion recently about older CONNECT:AMPs and difficulties that may be associated with failing memory modules. These devices are ancient, in electronics terms, and tech has come a long way. 

I would absolutely be confident in purchasing a Sonos Amp today. 

I have one since it came out in 2018. It gets used for hours each day. The hardware still works like the day I bought. It’s expensive but imo my best Sonos purchase. 
The model is 6 years old now, doesn’t have ace compatibility. Personally I would hold off if I was in the market if priced at retail. But would buy with a big discount like 30%. just my opinion. 

The flash memory will wear out eventually but Sonos has added enough spare memory that the internal error management should be able to deal with the wear related issues for many years, so I wouldn’t worry.