I'm not sure about if it is just sprain or much worse injury. He really did fall awkwardly. The thing with Boston is that they're deep so even without Tatum I think that they can do better throughout the rest of the regular season and then let Tatum rest and maybe come back in the playoff.
Only few games left, the standing specially in the West are very close. Every team in the 4th down to 10th really need to win their last remaining games at least in the contention for playoff. I expect that there will be games that are going to be very close and we will have playoff atmosphere already.
I quite agree that the Tatum's injury could have been a lot worse than just a sprain for others or in a different case because he did fall and twisted his ankle but I think it's not something serious enough to see him miss as far as the first rounds of playoffs, even though Celtics might decide to shut him down for the rest of the season. Tatum was able to put some weight on the ankle to shoot the free throws and then he walked towards the locker unaided, although he was limping but the he walked in my opinion indicated that it's not as bad as it looks when he fell and was writhing in pain.