I don't think we need to go to that extreme, Potatoe. The M's building is only 66' x 66' (not counting the canopies) with the street facades still intact. The overwhelming majority of people just want it returned to something resembling what it once was, with the same functions. Whether that is a complete restoration/duplication or something new that will blend-in with the Old Market remains to be determined. I could be wrong, but I don't think the Mercer's would take the approach of doing some new radical design, such as a Frank Gehry building, at that location. There would be a public outcry if they did, but people would eventually get over it.
In 2004, there was a fire in the old Egg building on 12th between Howard & Harney, which was being converted into a new restaurant/bar called Jobber's Canyon Brewery (now Blue). The damage from that fire was very similar, with some walls collapsed, and they were able to save the building. I think the key question now on the M's building is whether the remaining brick load-bearing walls can still carry the floor and roof loads, or if they will have to add new steel structure to shore-up the brick facades. If they have to add that much new steel, it might be more cost effective to start from scratch. Whatever they do, the new construction will have to meet the current building and life safety codes. I would assume they'll also add an automatic fire sprinkler system, and hopefully make sure the gas shut-offs are easily accessible everywhere in the old market. On the other hand, If they are allowed to just make repairs to replace all fire-damaged components to its original state, there might be some exceptions made as far as bringing it up to current code and ADA accessibility standards.
If they do need to build something entirely new, there is a great example of what could be done as an appropriate replacement right up the street at the southwest corner of 12th & Howard....