On a serious note, the slams that he missed due to injuries are RG 2004, AO 2006, Wimb 2009, USO 2012, AO 2013, USO 2014 and Wimb 2016. The slams that he didn't miss but in which he got injured: AO 2010, AO 2011, AO 2014, RG 2016, AO 2018 and USO 2018.
Nadal's chances of winning each of those aforementioned slams:
1. RG 2004 - slim to none. Still too young and inexperienced.
2. AO 2006 - zero chance.
3. Wimb 2009 - slim.
4. USO 2012- moderate chances.
5. AO 2013 - zero chance
6. USO 2014 - good chance. Although hot Cilic might be problematic. Lesser players have pushed Nadal on HC, so Cilic is in with a realistic shot.
7. Wimb 2016 - zero chance
8. AO 2010 - slim. Nadal was getting outplayed by Murray even before the injury occurred.
9. AO 2011 - zero chance.
10. AO 2014 - great chance.
11. RG 2016 - great chance.
12. AO 2018 - slim. Fed simply had his number on HC. And even before the injury, Nadal's form wasn't spectacular.
13. USO 2018 - zero chance.
At best, Nadal would have added just 4 additional slams: USO 2012, AO 2014, USO 2014 and RG 2016, which would put him at 21 slams.
But then, you also have to take into account that Fed too could have won more slams without his own health issues, like Wimb 2013, Wimb 2016 and USO 2016. These 3 slams were very likely to be won by Fed given the opposition in those and if his form was good enough, which would put him at 23 slams. So Fed would still be the GOAT IMO.