According to Making Star Wars, Finn has been placed in a bacta suit to recover from his injuries.
A mysterious shot from the Rogue One: A Star Wars Story teaser trailer seems to show that a bacta tank will appear in the spinoff as well.
Rogue One: A Star Wars Story opens in U.S. theaters on December 16, 2016, followed by Star Wars: Episode VIII on December 15, 2017, the Han Solo Star Wars Anthology film on May 25, 2018, Star Wars: Episode IX in 2019, and the third Star Wars Anthology film in 2020.
Making Star Wars has an image of what it might possibly look like.