We already retired EF-111s. B-1Bs were retired because of high maintence and operations costs (money saved is used to keep the rest flying) B-52Gs would need new engines. Why not just use some old 727s or 737s retired from airline service? They can go anywhere a BUFF can, expect down low, and an EB-52 wouldn't be doing that anyway. I think we need all the -Hs models to remain bomb droppers. The coming conflagration may prove their numbers insufficient as it is.
For the same reason they aren't still flying on 727s and 737s. They are much less efficient than new engines and require lots of maintenance. It would be better to lease new engines bundled with maintenance contracts if the DOD can't find the cash to buy them.