No.

Now you're just plain wrong.

Since when is Nintendo oversaturating the market with a lot of crappy releases. Where is Nintendo's E.T.? Atari led themselves to their own demise. In this case, Nintendo going out of the console business and becoming third party does not lead to "demise".

First off I would buy the console where I can play Nintendo games.
If I have to choose between Microsoft and Sony, I would go with Microsoft.
I'am a die hard Nintendo Fan and so are my sister and my girlfriend. Christmas 2009 I bought my sister a PS3 and my girlfriend a 360. We played some games on PS3 and some on the 360 together. Alone I played more on the 360 because I live with my girlfriend and for some reason I really dislike sony. Maybe it would be different now, if I bought the PS3 for my girlfriend, but who knows. This generation is really hard for me, my brain says buy a PS4 it has more games and my hard says buy the One. Many times I was really close to buy one of them, but I never went through with it. I'am also a member of the pc master race and this generation I was able to play more of the "good" games than before. I don't know which console I will end up buying, for now I'am happy with the Wiiu + PC combo. If Halo 5 had a splitscreen mode I would have bought the One for sure...

Many new hardware players enter the game industry theese years.. and even if you only look at games.. Sony/Nintendo only has like 5 games in a weekly avrage top 20..

And I have yet to see your proof for this. What is a "Nintendo looking game"? How does a "Nintendo looking game" look? How do you know Nintendo's games won't sell well on Steam? Because given that Nintendo hasn't released any games on steam, surely you really have no proof for this.

In the real world it would be neither of these options, because Nintendo would likely make a partnership with Disney or Apple first. Two major corporations that have enough cash to take Nintendo IP's to another level! Which seems like where Nintendo wants to moving forward with the NX and into the future.

Look at Amiibos for instance and how they're selling, this wouldn't be possible on Playstation or Xbox for Nintendo. Games like Pikmin, Fire Emblem, or Splatoon would never have been made and the only titles that would remotely sell well would be Metroid and Zelda and that's as long as,they have some realistic appeal to the visuals. So a Nintendo that only makes realistic looking Metroid and Zelda titles just doesn't sound that appealing to me...

So what you are saying is that Mario games and every Nintendo game that doesn't have realistic graphics would stop selling if the console it was released on changed name from NX to PS5 or Xbox Next? Would all people that currently buy Nintendo games dissapear?

Is Mario such a weak IP that it would collapse in sales only from shifting to a console made by another company than Nintendo? (hint: no).

Nintendo wouldn't align with Disney or Apple or Microsoft IMO because they're all massive American corporations that could then buy Nintendo out and do whatever they wanted with Nintendo IP and their staff.

Sony isn't big enough to be able to buy Nintendo and they are Japanese. That's probably the direction they would choose overwhelmingly. They could more or less just continue to function as they are now allied with Sony.

Look at their smartphone games even, they could have partnered with any larger US/Euro smartphone maker, but instead they choose to go with DeNA, a smaller Japanese company. 

What I'm saying is that if Nintendo ever got to the point that the OP is describing to need to merge with another company.  The Nintendo we know today would cease to exist and yes I'm stating that most of Nintendo's core franchises would not make the transition simply because Playstation and Xbox gamers generally look at Mario games as kiddie. Just look at what most people on the Internet do with Mario in UE4, it's nothing appealing to the franchise for sure. People who think that Nintendo wouldn't work with Disney or Apple probably haven't heard the news of them working with Universal Studios then. 

But what you say about what Playstation and xbox gamers think about Nintendo titles are irrelevant. Where do you think Nintendo fans would go if Nintendo merged with either Sony or MS? They would obviously either buy a PLaystation or an xbox, to play Nintendo games. Or do you think all those Nintendo fans would just cease to exist, or decide to quit gaming all together? Because that's the only way sales of core Nintendo franchises would drop if such a merger were to happen.

Also, if Nintendo had to pick a few franchises to work with, from sales, I can assure you Mario would be one of them, while Metroid wouldn't.