Do we know exactly what happened to them all? (Other then 343 and 04 monitor)
There isn’t anything suggesting they are doing anything other than their job.
> Do we know exactly what happened to them all? (Other then 343 and 04 monitor)
343 was the I04 monitor
Well, ONI uncovered Installation 03, which had one certain Monitor (The one that Spark talks to the Terminals, which states the Forerunner’s should be forgotten). So it either went rampant or it did nothing or even assisted ONI found Installation 03.
03-049 Abject Testament: Status is unknown. ONI has a research facility in orbit of his Installation so it’s possible they have been or will be in contact with him.
04-343 Guilty Spark: KIA, should not be confused with the Chakas Monitor from Primordium.
05-2401 Penitent Tangent: Status is unknown. He was last seen captured by the Gravemind but his whereabouts after the Gravemind left Installation 05 are unknown.
It is unknown if other Halos have been found so it is unknown what has happened to their Monitors as well.
Most Monitors are likely doing their duties as Spark was. But we can safely assume that most of them are reaching some kind of point of rampancy.