Whether Indian students were replaceable or not, we will get to see this year I guess. The number just hasn't gone down by 20% fyi, it has gone down by 80% in terms of new students coming to Canada last quarter. This is a massive shock that Marc Miller himself admitted in a recent interview. There's also a concern that lack of students could cause a recession in Canada. Right now a million TRVs are extremely vocal about their negative experiences with Canada which is hard to ignore.
Given that most students are somehow selectively exposed to the worst things about Canada(slumlords, bad employers, etc) and miss out on a lot of good that Canada has to offer, the dip in interest to study in Canada is organic. Had Canadian govt intervened at the right time, this would have never happened.