I believe that there are two reasons for dehiscence, one is increased intraabdominal pressure, as stated. The other is a technical error, most often pulling the sutures too tightly, and strangulating the fascia.
In the former, there is always frank evisceration. the bowels are found on the bed, and closure is difficult, if not impossible. These cases should be managed along the lines suggested. Tight reTension (with the emphasis on tension) do all the bad things others have described already, and may kill the patient in more than one way (I have seen them cut the small bowel in half) so should never be used IMHO.
If the dehiscence was due to a technical error, with the original sutures strangulating the fascia, primary reclosure is possible.
In the case, the dehiscence was local, the bowels just peeked through the open fascia, and were not pushed out. I therefore think that the dehiscence was due to a technical error. Although the amount of tissue lost by the necrosis may require mesh closure, it may be possible to close primarily, but the risk of necrosing the fascia again is still high. In this case, LOOSE retension - not tension- sutures, can prevent a third trip to the OR in the early postop period, while if the new suture holds, they do nothing. So, I would put them in.