navien tankless np series

So the back story is I bought this unit six years ago and installed it myself. Everything was fine till a week ago when it faulted out. No biggie, I turned on the electric backup and went looking for the best tech in the hood. He came out and diagnosed some leaks at the O-rings which he fixed, the death blow was the mixing valve is bad. The tech removed the sensor that faults over the mixing valve and fired it back up and we were off and running. I have nothing but good things to say about the tech. My question is going forward. The tech said he would be reluctant to spend on replacing the mixing valve given the age. Again love the tech. The hot water supply to the house is fine without the mixing valve. what is the harm/danger running the unit without a mixing valve? No kids, no old folks, just me and the better half. Initial thought is to run it till t dies and then replace. What say the folks more experienced than me?
Eric

Sorry to hear that your system has malfunctioned and your issue with the replacement. My plumbing team whom I contacted for my (edited out this spam) was a good team and they did provide replacement for the defecit parts, when I encountered something similar.
But then again, the heater at my place was younger to yours in 4 years.
As per your question of continuing with the heater, I would suggest you to take good care and control your water’s heat. This mixer is the part which controls the temperature of the water flowing through. Without it, the usage may turn hazardous even to you and your partner.