It was impossible to save the towers. If they weren't moved, they'd now be in the centre of the new pitch (the whole stadium's been shifted slightly).
The towers themselves were also solid concrete - so it was impossible to dismantle them and move them somewhere else. When this whole thing started, the FA did offer the towers to any organisation that could come up with a viable plan to move them for a token amount of money (something like £10). However, the logistics of it made it impossible.
I'm sure the plaques on them were saved though and I suspect they'll be displayed either somewhere in Wembley or move to the new Olympic Stadium in Stratford.