Did similar on avionics boards, where you could not get to the bottom set of leads as there was a package in the way on the other side. Snip the leads off, and then polish the inner side to bare base metal and solder the new chip to the stubs using stubby leads. The boards were made by applying solder paste to the holes, then placing the 400 odd dip packages to the 20cm by 15cm board on both sides then doing a vapour phase reflow of the whole board. No way to repair other than by that method, as they were regarded as basically throw away items, with a price tag that was about the equal of that mass of Platinum. All 0.1 in parts, and spaced at 0.1 inch on both top and bottom, along with being a 16 layer board with a few power and ground planes, as there were 2 5v rails per board. Most of the time fixing a fault was by playing mix-n-match to get a set of boards which would time with each other reliably over temperature. If wrong it would fail when cold and work when hot, or do it the other way around.