Good questions. The bottom line is that, with Nintendo's policies, you will likely someday lose access to all of the digital games you bought from them. I find it ridiculous for that to be the case however.
With physical media, it is understandable that you may someday lose access to what you have purchased. Think about music. Physical media like vinyl records, cassette tapes, and cds can wear out, break, and get lost or stolen. But when you buy digital music, it is never going to wear out, break, or get lost or stolen. Even if the company you bought the music from goes out of business, you can download the files and back them up to as many devices and cloud services as you want. You buy it and have it to enjoy for the rest of your life.
The nature of digital solves the problem of losing access to what you have purchased. That is unless you implement awful anti consumer policies that ensure people will someday lose access to their purchases like Nintendo has done. There are alternatives. Sites like GOG and many others offer tons of games DRM free. I can't stand to buy a digital game from Nintendo anymore because I feel like such a sucker doing it.