Microvenator, as seen above, is based off of loosely related and, though it looks as though it is articulated, disarticulated fragments of bone. The skull has only been found in small chunks and the holotype used by Ostrom to describe the animal was only about half of a mandible, if that much. Therefore, any representation shown is an educated guess based on the description of Microvenator and subsequent taxonomic relationship derived thereof by Ostrom in his 1970 publication. Ostrom, of course, was not a slacker and his description is well thought out, thorough (for the time at which it was produced and published), and as exhaustive a description as it could be based on the fragmentary evidence available. Two basic models of the skull have been generated based on the description of Ostrom and the fragmentary evidence of the skull that is available including any newer materials that have been weathered out of the soil and collected since 1933 and 1970, the original discovery and description respectively.
One mode of depiction of that skull, best exemplified by this slightly older illustration, is that of a longer muzzled theropod. Based on the bit of mandible that was discovered in the original fossil grouping, the muzzle would extend a little but further forward than in other Oviraptorids, and this would not necessarily be incorrect. Remember that Microvenator is considered to be a rather primitive, or basal, Oviraptorid and may have thus retained a longer muzzle, even though it too may have been mostly beak like and toothless such as that found in later cousins and descendants of the species, as it was just recently divergently evolving from the other Maniraptors it is cousins with. Somewhere that face had to have changed over from the Maniraptor muzzle of a long toothy death machine to the more bird-like beak of the Oviraptorids and Microvenator, being as primitive as it is considered to be, sounds, and looks, like a fantastic place for that change to occur.
The more recent version, however, shows Microvenator having already developed the bird-like beak of the other Oviraptorids. While not outstanding or ostentatiously strange, this sort of skull would assume that A) the fragmented mandible was indicative of a bird-like jaw structure and B) that there is an even more primitive Oviraptorid or Maniraptoid form that is an intermediary between the Maniraptorid muzzle of sharp killing teeth and the toothless Oviraptorid bird beak. As with anything in paleontology, that is quite the possibility, but given the justification within the description and subsequent debates over the placement of Microvenator within the basal Oviraptorid slot it is difficult to think that Microvenator is not that intermediary between bird beak and toothed muzzle. However, the, so far, complete lack of sharp killing teeth associated with Microvenator does support the bird beak idea, which would allow for the diet of Microvenator being close to that of Chirostenotes and other Oviraptorids, namely consisting of small mammals, lizards, and vegetarian delights additionally, and make the idea of Microvenator as basal, but not the intermediary between true Maniraptorid and true Oviraptorid dinosaurs, hold a lot of water, figuratively of course, when depicted with the bird-like beak rather than the elongated muzzle.