I think they will. A5x is still very fast, and it'll run even faster on the smaller screen. Besides, it'll help to keep the price low. My guess is regular 9.7" iPad 4 will get A6, but that's not gonna happen until next year. Next week event will be all over iPad mini.
I think that the A5X is pretty unlikely. It's the same CPU performance as the A5, just more GPU cores and bandwidth to handle more pixels. It's a physically large chip, as well as being relatively expensive because of that size and very power hungry. Most of that is because it's still being produced on the older 45nm process.
The new 32nm A5 that's being used in the $399 iPad 2 and new iPod touch has the same CPU power, plenty of GPU power to handle 1024x768, and is smaller and more power efficient than the original A5 and much more so than the monster A5X.
I haven't seen any rumors about the A5X going to 32nm, so I think the 32nm A5 that has been in production for several months already is a safer bet.
An iPad Mini in the $300 range with the same performance as the iPad 2 in a smaller form factor with great battery life will be a great product.