Unfortunately, such a sledgehammer-and-fly solution is bound to have some undesirable effects on the ecosystem of the river... I hate to be a downer, though, and I really envy the creative thinking of those old engineers.
I'm sure, if the bridge is ever refurbished, it will simply be thoroughly documented, cut up, and put back together, with new pilings drilled. For all of our sakes, I really hope the foundation contractors are careful - especially in this area...
As far as the Division Street bridges go - is it possible that they could be re-used at Taylor and Polk Streets, where the city specifically needs new bridges? I brought this idea up awhile ago, although I'm not sure anybody commented on it. I assume the bridges no longer work at Division because they are 2-lane. 2-lane bridges, however, are exactly what's needed at the bridge sites in the South Loop.