Eh, I'd say about 30% or so. There are quite a lot of Nintendo fan projects like this that do fine for years; this one's been in public development for nearly a decade now.

However, there is a possibility that a fake take down might hit it. There have been stories about someone pretending to be a Nintendo lawyer and randomly taking down fan works, or maybe some sort of bot auto removing stuff under questionable premises.

For example:

https://www.youtube.com/watch?v=m_gnwn535eM

Or my post about the same matter:

https://gamingreinvented.com/nintendoarticles/fake-nintendo-...

However, it's not as likely to take it offline as for some projects. The imposter only seems to go after file hosts like Dropbox, Mediafire, etc. This fan game is also hosted on a Metroid fan site and isn't dependant on a company honouring questionable takedowns to cover their backside.

It might happen, but it could easily survive. Or have its mirror links taken down by an imposter.

I'm not really sure you can really put odds down on something like this. For the Youtube things, you are right that Nintendo has had a very unusual track record with videos. For example, while Let's Plays have been removed, things such as Angry Video Game Nerd and Pat the NES Punk continue to operate without issue. To the best of my knowledge, neither has an agreement with Nintendo, and they utilize Nintendo IP very heavily.

Additionally, with something like the Mother 3 translation project, Nintendo was apparently "aware" but took no action. [1] I would assume there were similar conditions for other translation projects for Nintendo products. I think in the case of Mother 3, it helped that it had been officially decided there would be no official translation at the time and the translation team plastered commands about "don't pirate" and links to purchase the original game via import all over the site.

This fan game really isn't quite either situation - it uses Nintendo IP, but it's also 100% from the ground up original content and code, so it's just the Metroid IP that Nintendo could issue a cease and desist over. AM2R has been in production for years though, and I don't think it's been any secret to Nintendo. My guess is if they haven't issued a c/d yet, they probably are giving a silent approval.

[1] - https://en.wikipedia.org/wiki/Mother_3_fan_translation

edit: forgot my link >.<

It uses their intellectual property and content Game Boy Advance versions of Metroid. Chances are Nintendo will take it down same as when they killed the remake of Mario 64.

And Chrono Resurrection... https://en.wikipedia.org/wiki/Chrono_Resurrection

Mmm, this was Square Enix stopping it though, not Nintendo. Nintendo was silent on the Chrono Resurrection project.

Seems to have happened on both the share-site links on the page, sadly.

And sadly, seems that the torrent isn't working [for me].

torrent still seems to work