The problem isn't the original rule, or the possible retraction of the temporary exemption of that rule. Of course at some point it will be retracted. It was, however, instituted for the purpose of dealing with a state of emergency, which is still officially in place. The government has some leeway in policy making, but capricious & unreasoned decisions can be struck down, and this could fall into that category given the circumstances that produced the policy still obtained. (Regarding capricious/unreasoned decisions, see also the Supreme Court's recent ruling on DACA: It was not because the SC said DACA couldn't be eliminated, it was because the policy change did not go through the legally mandated process for such changes)
The problem was also the timing. Students under an F1 visa must remain enrolled in an eligible program. If they are not, they have 60 days to leave the country. College semesters often end around mid-May, we're in mid-July, meaning as of the date of this announcement last week, students in online courses had already failed to be enrolled in an applicable program for nearly 60 days and would have a week or three to pack their bags and leave the country.
Before that, they could try to figure out if their mix of online or hybrid courses qualified as sufficiently "in person". This was without formal definitions from the administration of what constituted a sufficiently "in-person" course with respect to hybrid courses: The general policy was announced but there was never any official posting to the Federal Register that detailed the definitions, limits, exceptions, etc. In the announcement, such details were promised, but never materialized.
So, students had 1-2 weeks to panic and determine if their schools:
1) had any in-person courses
2) if so, determine if any applied to their program
3) If 1 & 2 were a "no", find, apply, get accepted, and register at an alternate school with applicable in-person courses
4) Having spent time on 1,2 & 3, vacate the country within a handful of days.