Not terribly useful. A B-52 without jet fuel, lubricating oil, or a decent airfield is just a big funny-looking metal structure.
Assuming they do have enough fuel, a good enough runway (which would require new tech in its own right, unless a B-52 can take off from a big dirt field) and at least conventional munitions, whichever side has it wins handily. Being able to fire-bomb Richmond or New York has its advantages
.