1 AO 1 W 1 more US for 4. I think he will be relevant at four more AO and 5 more of the rest, so 3 of the next 19.
If he does not manage this, that implies a couple possibilities:
Novak and/or Nadal coming close to Pete Sampras.
Nadal coming close to Federer.
Federer coming close to 20 career slams.
Or, least likely, a new guy becomes a consistent slam winner/finalist in the next couple years.
Any of these scenarios would be interesting.