There will likely be two law suits before SCOTUS:

1) (Texas lawsuit) Was DACA a substantive rule requiring a notice-and-comment period as required by the Administrative Procedures Act or was DACA a general policy statement (where no notice-and-comment period is required)?

2) (3-way lawsuit) Was DACA ended properly? You can't change agency rules for capricious reasons.

The best outcome is if DACA is ruled a general policy statement that was ended improperly. All that means is that DHS just needs to go through the proper procedure and end DACA that way. At this point DACA could be immediately terminated for everyone, terminated for everyone in X months, or the gradual rollback continued.

The worst outcome is if it's ruled that DACA violated the APA meaning that it should have never existed. In that situation the program could be terminated immediately and status cancelled for everyone.

The Hanen 117 page ruling lays out a pretty good explanation of why DACA should've followed the APA, but the second, 6-page ruling says that it could still be argued otherwise.

Edit:

Reading the complaint filed by Texas is also interesting. They cite King James II from 1688 and talk about how the US constitution is built on the idea that the executive branch doesn't have the power to dispense (get rid) of existing laws.