Where would Nintendo be at now if the original Wii failed and sold about, lets say 25m?

They would either:
A: Try to find another gimmick. Or
B: Do the same as Sony and Microsoft are doing.

It would have been more likely they would have taken the second route.

The only thing that is sure is that they would not have named it the wii u.

Impossible.

But IF it happened then .........this gen would be the casual gen.

Well in terms of profitability Nintendo would still have been fine during that time since Wii was sold at a large profit in addition to the huge profits from DS.

In terms of hardware strategy im not sure what they would have done, would the Wii U be what we know it as today or would they have tried reinventing themselves again?

Call me when that happens.....
(Srsly) Probably as Sega, only games no consoles. If not, more portables. If not, just another console that is similar to Sony and Microsoft consoles

They'd either do what the PS4/XBO are doing, or do the exact same thing they did with the Wii U but without a GamePad.

The end of the industry...

I was being sarcastic, dang should have added jk at the end... Anyways, Nintendo would have stopped making home consoles all together, as they said they would if another console underperformed like the GameCube . IF Wii was a flop, no more Nintendo home consoles. They would be all about handhelds. It might not be the end of an industry, but it would be a tremendous blow.

Nothing really. Wii did fail at least in retaining its core audience. So nintendo would have been in the same scenario that they are right now with the wii u.

Maybe they'd decide to release hardware that would compete with the PS4 and Xbox One, allowing them to bring in all those third-party multiplats, AND still release their Nintendo-y first-party offerings. I mean Jesus, can you image a Wii U that could run all the third-party stuff AND had the advantage of Nintendo's extensive exclusive offerings? o.o That could actually be a force to be reckoned with.