No. Councils cannot depose popes.
.....
Though a Council could declare him a non-Pope.
Yes, that's what I mean by depose. A council could declare a pope a heretic.
Right. Of course, the problem is this: Who but a Pope can legitimately convene a Council? What Pope would convene a Council to determine whether they should declare him deposed? Now back in a less abnormal time, when you had the scenario of a single wayward Pope and where 99% of all Catholics would recognize his heresy, that could work. Now, however, if Cardinal Burke tried to convene such a Council, you'd probably have at least 95% of all Novus Ordo prelates refusing to participate because they would back Francis. So if the remaining 5% gathered in Council to declare him deposed, would that constitute a true Council?
I'm afraid that we're in a major pickle here that only God can fix.