Am I being a bit naive here - why didn't the plane just carry on with 3 engines until it got to SG ? Today 01:53
May well not have had enough fuel to complete the journey at the lower levels, (3 engines now working harder than 4), then it would have been required to land and once on the ground it will, in all probability, stay there until the engine has been changed.
The crew would certainly have contacted Singapore and that will be where the decision came from. Send it back to Paris where there are other crew, possibility of other company A380 in the region etc. etc. also get the passengers off to London, Amsterdam, Frankfurt etc. to continue to Singapore on other SIA services, the list is endless.