I’m not sure if you can do firmware update on the OPN via the NoahLink Wireless or not, though. You may need the old wired interface for this. But at least with the Oticon More and going forward, the NoahLink Wireless is the ONLY compatible interface for programming the More, so I presume that wireless firmware update via the NoahLink Wireless is possible.
The old OPN models haven’t had any more firmware update for a long time now, and most likely won’t anymore, so it shouldn’t be a big deal for the OPN anymore if you lost your wired interface. However, if you buy replacement OPNs from eBay and they’re not on the latest firmware update, then that’ll become an issue for you, unless the seller can tell you what firmware update that device is on.