From what I’ve read, there were spare seats.
But apparently the dead woman was ‘very large’, so I can’t help wondering whether the couple in question - very taken aback, in shock - were then unable to get out, if the woman was in the aisle seat.
I’ve had to climb over a very fat person who was asleep in the aisle seat, stepping on the armrests! - in order to get to the loo, but not everybody is sufficiently agile. But that’s why I invariably book an aisle seat nowadays.