The "Pillars" can be fixed with a Plastic Weld solution, which can be purchased from any good model shops, apply to both sides to be bonded (it melts the plastic and bonds them together). In regard to the broken rivets, well consider yourself lucky for not needing to break off more when you decide to do a "Nuts and Bolts" mod.
I had 2 NIB Mini Spacesavers shipped from US and both have more than a dozen rivets broken, they just do not travel very well. In my opinion, if you wish to preserve/improve/etc/etc/etc an IBM M, then it is best to do the "Nuts and Bolts" replacement.