From Genalogics.org:
"Heribert died before 762, as stated in an act of his daughter and son-in-law." - found under 'Notes / Biography' on this page:
http://genealogics.org/getperson.php?personID=I00020920&tree=LEO
From the Medieval Lands project (fmg.ac) it is clear that he still donated land to an abbey on 23 Jun 720. By 13 Aug 762 his daughter Bertrada donated property to Kloster Prüm, and it is clear that he (Caribert) is no longer alive. http://fmg.ac/Projects/MedLands/FRANKSMaiordomi.htm - see paragraph H 1b Charibert.
Somewhere between 720 and 762 thus seems to be his date of death. Could not trace April 747 anywhere (so far) though.