Honestly I think that Supreme Court would issue a stay and would uphold that DACA wasn't illegal. DHS v. Regents wasn't about the legality of DACA because nobody asked the court to review if it was legal in the first place, it was only an argument regarding "Can it be ended the way it was ended".

Deferred Action existed in some form since at very least 1970s where John Lennon's lawyer managed to make information about it public using a FOIA, it's acknowledged in some laws (like the RealID Act), and DACA isn't even the first blanket exercise of Deferred Action, you also had:
1. 80,000 Chinese nationals granted Deferred Action after Tienanmen Square under Bush Sr., eventually superseded by Chinese Student Protection Act
2. 1,500,000 granted Deferred Action as part of the Family Fairness Program under Bush Sr., eventually superseded by Family Unity in INA 1990 and LIFE Act of 2000.
3. Deferred Action to people who might be eligible for VAWA if it passed (Unknown amount) under Clinton, eventually superseded by VAWA, technically still ongoing since USCIS will grant you Deferred Action if your I-360 is approved.
4. Deferred Action to students who were affected by Hurricane Katrina (unknown number) under Bush Jr.
5. Extended Deferred Action to Widow(er)s of US Citizens and their children under 21 (unknown number) under Obama, eventually superseded by a court settlement and congress removing 2 year marriage requirement.

Family fairness itself was almost double of however many people were ever granted DACA (around 825K).