So what do you think that Microsoft can do to save Xbox? 

It's very much alive in the UK at least.

Very little information in the OP. No offense. Need more information.

This

I think they're on the path right now. The fact that their consoles are one upping Sony is probably the first step.

If NX is more of a portable device, I think MS should throw a ton of money at Nintendo and let them have a stake of the XBOX brand (ie Nintendo takes over distribution in Europe and Asia). Nintendo also gets a cut of licensing fees from XBOX.

MS could agree to also supply games for the NX, since it's mostly a portable/mini console potentially they are different enough products.

Nintendo could have games on iOS/Android, Xbox, Windows while having their own NX platform. Good exposure for their IP while still having good amount of control over hardware.

Honestly, I think losing in the U.S. caught them and everyone by surprise.
They probably expected to coast there and focus on building Europe but instead ended up having to fight for lost ground in the U.S.

Give up on Japan

Make a FIFA bundle and have it price 100 dollars less than PS4 for Europe.

So Nintendo games on Xbox ?  Or Nintendo in charge of Xbox hardware in Europe and Asia?  I got lost in what you're proposing. 

Put the consumer first as gamers, cater to gamers, and don't just target the biggest audience of mindnumbed masses that they can find while dictating to them what they want.