Fed definitely still has plenty of chances to win 1-2 more between the AO, Wimby and USO (the long drought at the USO has been due to bad luck if you ask me and a title is overdue).
The question I have though is whether Fed still has the motivation. That loss in the Wimby final was tough to swallow, and his hiccups in the early rounds of the USO may have been a sign of that. Then the bad luck of getting injured ahead of the Dimitrov match at the USO. If I were he, the realization that so many things have to go right in order to win a Slam (a decent draw, staying healthy for two weeks, not running into a zoning young player or even an in-form Djokovic) would be very daunting. And even if the stars align and he does win 1 more Slam, Nadal could still surpass him given the gap is so small. Summoning that final push when there may be nothing more than an empty pot at the end of that rainbow could prove insurmountable.
I think we will get a good indication based on Fed's body language and form in the remaining months of 2019. If he looks good and looks ready to make a big push in 2020, I think he can win 1 more for sure. His level in the Wimby final was incredible and if not for nerves during the tiebreaks, he actually had the higher level for most the match and would have won.
But to stay motivated, to keep staying mentally positive and training hard, doing injury prevention exercises and all that, when so much of the outcome of the Slam race is now out of his control, it's really hard to motivate oneself under those circumstances.
