In the short term, I think Arduino's hypothetical discontinuation of the Nano would only encourage 3rd party manufacturers since it means Arduino will no longer exist as a competitor for sales of that board.
If you see the hypothetical discontinuation of the Nano as a step towards an eventual phasing out of the AVR architecture, then I would agree that in the long run that will lead to lower production of those boards but I'm sure as long as Microchip is still selling the chips someone will be putting them on boards. Certainly Arduino has not created a new AVR board for some time, unless you count the Uno WiFi and Leonardo ETH boards created by Arduino.org or the Gemma board created by Adafruit, all of which seem to have gone by the wayside quite quickly. But as far as the community, I think the AVR is still by far the most used architecture and the best supported. As long as these chips continue to meet our needs (which they will) and Microchip continues to manufacture them (which they will), the AVR will continue to go strong regardless of whether Arduino decides they want to make money selling them. Heck, Microchip/Atmel is has recently been releasing new AVR parts. The ATmega328PB is pin compatible with the ATmega328P used on the Nano and that chip is already available on Nano form-factor boards.
I agree that the Nano is the ideal board for a beginner. That's the board I'll be giving my nephew to get him started as soon as he's old enough.
falexandru:
more expensive because of useless capacities
Well, to be fair, a lot of the new microcontrollers are actually significantly cheaper than the Nano's ATmega328P. Even more so when native USB allows them to replace not only the ATmega328P but also the FT232 USB chip. But I'm certainly happy to pay an extra couple dollars for the good old AVR.