In general electronics will fail, all you can do is keep it cool, avoid static electricity and hope for the best. Static electricity is another reason to think twice before using compressed air to clean electronics. The MTBF rating dropps off relatively quickly with increasing temperature, but for more insight I'd defer to the Duet3d guys.
To address the Duex2/5 question, it would likely work as you describe the remaining drivers working, but depending on the root cause for the initial failure its a game of chance with respect to future failures. I'd check out the warranty terms with my supplier, then try to find someone to replace the €6 driver chip before considering the Duex2. For maximum reliability I'd get a new Duet.
