As I'm sure you remember Saeed. The 777 was shutting down engines at an alarming rate for awhile when new. They'll get on top of it.

I don't think a decent of 500 feet in a minute is unusual.

The single engine service ceiling of most twin engine airline aircraft is somewhere in the mid 20's...so if they were cruising at 35000 ft or so, which they would have been, at maximum continuous power on the remaining engine, it would drift down to the mid 20's...which should have been explained on the PA...when they had time!
In other words, this( the 500 ft per minute descent) was not something to get her panties in a wad over.