Can apple tv replace my cable box? (Fios)

It depends on how you want to watch tv. What apps you want yo be able to use. Most of the network apps like FX, FOX, CNN etc require an active cable subscription in order to use the app. But if you primarily watch Netflix, Hulu, HBO etc then you can definitely cancel cable. You could at least scale back your cable "package" but you'd obviously want to keep the Internet account active. But it's not a replacement for the cable box itself. The cable box will "decode" the channels your package allows you to receive. The Apple TV a streaming device that allows you to selectively choose which apps you want to download and access. Very similar to an iPhone or an iPad but for the large screen in the living room...

one thing I forgot to mention is that we could see cable providers develop apps for the ATV. Sling already has a streaming only cable like service but have not released a native app for the ATV. But you could AirPlay from another device. So we could see devices like the ATV replace the traditional cable box but currently it's a standalone seperate device...

That's not completely accurate. the ATV4 has an App Store. Any content owner can design/submit an app. It has nothing to do with "deals" Apple may sign. Now if your referring to the long rumored subscription service that Would probably be accurate but since it's not been released it's only rumor...

the the apps available on the ATV4 have nothing to do with "deals"...

I'm happy to answer questions here.

you only get access to channels that apple made deals with and many such channels rely on you also have access to them on a normal network subscription

It will not replace a FiOS box.