What is the average life expectancy of a DAC?

I think there are two questions embedded in yours - one obvious, one hiding.

The hiding question is "how long until it is obsolete and [possibly to you] worthless".
The surface question is "how long will it operate reliably".

If you buy a quality DAC at the top of the food chain ( in its range) the answer is "quite a long time". While i have new/newer DACs and prototypes I’m working on (excellent, but have, uh, issues at this early stage, kinda like 2 year olds), i also have two very old DACs and both are useful.

One’s a circa 1999 (?) MSB Gold Nelson, with a bunch of modifications I made that improved it significantly. It works great, sounds "good" but not state of the art, and has a big flaw (to be corrected) - S/PDIF input only - no USB or network.

I also have an even older one; a Theta DS-PRO II from what, 1989? 2nd Gen of the DAC that started DACs. It was also S/PDIF only (duh, i came out when that interface arrived) and continued to sound pretty good. Again the bog caveat was that i needed a USB or network --> S/PDIF converter and most suck. There are a very few pretty good ones, like Mike’s Piece of Schiit, but it doesn’t play well with the Theta - they get in synch fights. Ironic since Mike designed both, albeit 40 years apart.

So i built and inserted a USB --> isolation --> re-clock --> clean power stage before the S/PDIG and stuffed it inside. Now it soudns much BETTER than it did, presumably with less jitter and ground noise.

I realize this is not a path most people can take, and normally i would not waste the time, but the DS Pro is such a piece of audio engineering history (look it up, very innovative and cool) that i just had to save it.

So the moral of the story is that within reason, they can both last and continue to be useful and good sounding - but tech may move on.
G

Hey if mahler is right on the inflationary cycle ( there is a global chip shortage) might be able to sell for more than paid....ha..
course don’t listen to me I have a Smithsonian basement full of obsolete tech DAT, HDdvd, VHS, SVHS, Nakamichi cassette anyone? 

Th electronic components will last a long time. The only real question is whether advancing performance will leave the high(ish) end DACs in the dust.    

But consider that the performance of a DAC will NOT diminish. It will stay the same (as long as the electronic components do not wear out) or maybe even increase as caps are used. So a given DAC will be as good in 10 years as it is today. It is only the improving performance of the competition that will change.  

just as a sidebar note...

among my little collection of dacs i have a 1997 vintage van alstine fet topp dac, employing the lovely philips tda1541a r2r nos dac chips and with tele 12ax7s... the old crystal semi input chip won’t read anything but a redbook input, but this thing sounds every bit as good as several well regarded current dacs i have tried in the $750-2000 price range, and a good bit better than numerous others i have tried...

Any electronic device will last as long as its worst quality or hottest running electrolytic capacitor.

If the design is proper, ie no other overloaded resistors exist, the first components which go are the electrolytic capacitors.

So, your DAC will also last as long as its worst electrolytic capacitor.

Good quality electrolytics will work up to about 15 - 20,000 hours at 85 or 105 degrees C.  Cheaper ones will give in earlier.  Your mileage may vary.