Would it be a big blow to Nvidia how would it effect them?

Clearly that's big money if Sony and Microsoft both go with AMD.

Most things I've read are more concerned with how this affects Nvidia

Intel will definitely be fine, I think the real effect will be on nVidia. Currently nVidia throws a lot of money into its TWIMTBP program which rightly or wrongly helps developers optimise their games to run on nVidia hardware. The current effect of this on how games perform on nVidia hardware vs AMD hardware is a bit unknown, through the Batman: Arkham Asylum anti-aliasing fiasco does seem to indicate that its borderline anti-competitive at times.

With all three consoles on AMD hardware, developers will not have a lot of choice but to optimise their games for AMD hardware, making nVidia's TWIMTBP program useless. I'm sure they'll take the money, but developing a game that will be less than optimised on AMD powered consoles (which generates the most money) doesn't make sense. The end result will probably be good from a fairness perspective, and hopefully force nVidia to compete on hardware alone and not game optimisations that have been proven at times to deliberately disadvantage AMD hardware and the gamers that use them (disabling GPU powered physx when an AMD and Nvidia card are both installed in a PC, as an example, even if the nVidia card is used to power the graphics).

I belive you're confusing Intel with Nvidia...but it won't be such a loss.
Nvidia is getting their stuff on tablets and mobile phones instead of consoles. So they got a replacement that could end up being more profitable.

Considering that Intel is like 8 times bigger than AMD and 20 times more profitable, plus intel haven't been used in a console since the OG Xbox I would say "not at all"...

Yeh I got Nvidia mixed up with intel, apologies.

Doesn't really matter, I'd say Nvidia got themselves in this possible predicament.

They'll survive anyway.