Roberts does have a legal out... because although Congress itself eliminated the mandate it left the rest of the law intact. That demonstrates legislative intent not to end Obamacare. The last thing Roberts wants is to find Obamacare unconstitutional. That would pave the way for a Democrat sweep in 2020, socialized medicine and the the slow death of the free enterprise system.
Link: https://slate.com/news-and-politics/2018/12/obamacare-ruling-texas-john-roberts-scotus.html