I really think Ozil is replaceable. If we get silly money for him we should just sell him on. He's not consistent enough in big games.
Sanchez? Give him whatever he is asking for and just sign him up. We cannot afford to lose the striker. Wenger did very well to convert him to a centre forward and to lose him would be a real bad thing for the club.
If Real were to offer £80m (which they won't, because Ozil would probably be benched) for Ozil we should take the money and buy someone like James or Isco. Really the only teams that would pay for Ozil are City and Chelsea, and really he would not be a big loss as we can buy a better replacement.
Out of the two, I think Ozil is not even likely to leave. But Alexis likely will if we don't win trophies or beat big teams in the CL.