I think SEGA would have went down anyway. They were Nintendowned. Seriously though we wouldn't have Halo and that would suck. Then again they could have made Halo on something else, but it's hard to tell.
Really though, there was nothing wrong with Microsoft making consoles. Until the Xbone.
From one side; Better, because I honestly think the Xbox, 360 and XbO don't bring much to the table, there's just no innovation, now uniqueness, and it's just plain old rehashed games with a slapped new number at it.
On the other hand, Worse, because Sony would've gotten away with it's poor decision making and would've never decided to improve this gen, Microsoft served as another good competitor to Sony in terms of sales, one which they needed badly to recognize they're in trouble.
Overall? Micro$oft should stick to Windows. (And not even that! Windows 8 is absolute crap!)
Better at a standpoint where we won't hear those annoying xbox fanboys saying their "xbox is better" crap. Speaking of which, fanboys suck (especially pc ones) so i'm pretty sure a removal of fanboys of a certain console would be better.