The ECU has a knock sensor and can pull timing to compensate for bad gas (or 87 octane). However, the pistons are sensitive to damage. General consensus is that knock events are likely to contribute to premature piston failure and its best to avoid them.
When I was buying my 2009 my dealer specifically warned me about using 91 octane. He told me about a 2008 FXT that needed a new engine after 50k because the owner used 87.