[souffle]

Well this is a really horrible situation that should never have happened.
For a start two syrians should not have been together EVER. They are naturally solitary and will fight if kept together.
It is most likely that a fight led to one killing the other.
Hamsters will eat animal flesh though they are primarily vegetarian so yes it would not be abnormal for one to consume a dead hamster particularly if it was lacking in food otherwise.
How on earth the fact one was dead and was not noticed till a week later when the flesh was rotting is beyond my comprehension. Hamsters need daily checking, feeding and fresh water. How was this not noticed? If it was sick it may have suffered and been in need of vet care.
The remaining hamster could become ill from eating the dead flesh especially if the other poor hamster was indeed sick. I would suggest a vet visit and a good check over to ensure everything is in order with that hamster.
Set up a routine now of good care and daily checks for this little one so it can enjoy the rest of it's life being attended to as it should.
Rest in Peace little lost one x