Devastator is an immensely powerful warrior, and in that sense the combination of the Constructicons into a merged being is a huge success. Mentally, on the other hand, he is very much less than the sum of his parts. Devastator's primitive psyche is limited to only the thoughts and actions on which all his components can agree, which results in raging bouts of destructive fury. Given the sheer power Devastator brings to these rages, Darth Grievous has no complaints.
The Constructicons formed devastator one last time on Korriban but they died in the hands of the Autobots.
Dark Future[]
In Darth Grievous's evil vision of the future Devastator was killed fighting the Autobots during the Autobots last stand against the sith.