In a peer war it's pretty damn dubious whether a B-52 with four modern engines will be more survivable than a B-52 with 8 antiques. Either way the most they'll be able to do is launch standoff munitions from a distance they hope will keep them safe, and if it doesn't then they're dead anyway. In a scenario short of that, we're just quibbling over the degree of waste American voters will put up with (it's the military, so the answer is a lot.)