or that some Islamist bomb(s) where so huge or so strategically placed that the plane totally disintegrated leaving no wreckage to be found;
or that somehow the plane was hijacked and taken down to near water level and below radar flying on to land somewhere.
One thing we may be sure of is, if this was terrorism, then whoever it was will repeat it soon - before their method is discovered.
There was a plot to blow up lots of planes in that area over the water all at one time.
I just assumed the “oil slick” stories included wreckage. If there was no wreckage found, it means nobody knows where that plane is.