The Hollywood Reporter has posted that Kevin Dunn is "in negotiations to reprise his role as [Ron] Witwicky in the third "Transformers" film." Key word in this case is "negotiations" as it gives rise to the possibility that a return may not occur. Doubtful but strange things can happen when an issue of money is involved. Assuming it all works out, this indicates that the Witwicky parents will return for more hijinks.
In this case, the issue at hand may not even be about money but scheduling conflicts as Kevin Dunn recently signed on to join the new HBO's new drama "Luck" starring Dustin Hoffman. It should be noted that when it comes to sequels, while most actors sign up for the typical three movies, re-negotiating the contract is common. Thanks to Christopher for the link.