No Derrick White, wow, that makes things tough but if we have Smart and he can play like Marcus Smart, I would not write this off.
Pritchard can play the back up guard (he did in Game 1 behind White). We will have to play with Smart and Pritchard together at times to allow Brown to get some rest. I am not that concerned in terms of the guard rotation but what that rotation does is limit how much Brown can play for Tatum to let Tatum rest. Nesmith will need to play 10-12 minutes again.
Here is how I see it:
Guards (96 min):
Smart (36), Brown (42), Pritchard (24)
SF (48 min):
Tatum (42 min), Nesmith (12 min)
Bigs (96 min):
GWill (36 min), RWill (28 min), Theis (20 min)
I know this doesn't add up exactly but it means there there will be about 12 min of small ball, only one big.
This is pretty much the same as last game except we hopefully will have Smart over White which should be an upgrade. This will be a tough win, we are playing Theis and Nesmith more than you would like (because of no Horford and White), and I guess Pritchard too, but overall, we are still not all that bad off. If we don't have Smart, White, and Horford, may as well just rest everyone and hope we can win 4 of 5 when we have everyone back.
The game turned out to be a rout so some of the numbers are off but here is how it turned out:
Guards (Brown, Smart, Pritchard) ended up playing exactly 96 minutes but it was Smart who played 40 min with Brown at 33 and Pritchard at 23. There was some garbage time guard minutes also.
Wings (Tatum and Nesmith) combined for only 39 minutes but there was some garbage time wing play. It turned out to be a light night for Tatum. That should pay off down the road.
Bigs (Horford, RWill, GWill) combined for 85 minutes. All played solid. The remaining big minutes were garbage time (Theis, Kornet). They played all of the meaningful parts of the game with 2 bigs on the floor. They did not go 1 big really at all.
With White back next game, he should take some minutes from Smart, Pritchard, and Nesmith. No one should need to be overworked. White has been averaging 24 min in the playoffs, Pritchard 15 min. We may see that split more 20 min / 20 min with Smart reduced down to more like 35 min and Nesmith likely 0 min.
Overall, I think things look pretty good for a team with such issues with depth and roster construction

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Seriously though, we have Theis (9th guy) as a decent player who we don't even have to play unless one of the bigs gets in foul trouble or something and then we have Pritchard as the back up to the back up (White) who is giving us outstanding minutes when we need him to. I will concede that our back up wing (Nesmith 10th guy) is not quite playoff ready but we can mitigate that with our guard depth that allows Brown to play wing when Tatum needs to rest and vice versa. During those times, we just play with 2 guards and 1 wing instead of 1 guard and 2 wings. And even Nesmith has been able to hold his own when needed the last couple of games.
Man, there are so many things that I would like to say but I am afraid to say them out loud due to my irrational fear of jinxes and all that. We cannot afford a let down after this win. We need to just keep it up. Miami is still a very good team. We can be lulled by this one easy game.