The entire island would not collapse into the sea. But a piece of it could.
Indeed, that does happen now and again. It happened at Krakatao a few years ago, where, without any significant volcanic activity, part of the island collapsed into the sea and a local tsunami did considerable damage along the Java coast.
I have two houses in Sulawesi, but in the south at Pare Pare and Awan Rantekarua, Toraja. I rarely go to the north side.