The BUF

[727Sky]

[hounddoghowlie]

as long as they can keep on rockin lobsters

[Wallfire]

Any A/C can be upgraded and virginised for as long as is needed, the stopping point comes when something better is found or its just too expensive to keep making it a virgin.
Like the Russian TU95 the B 52 has found it own corner, its not meant for front line warfare so  at the moment its cheaper that building a replacement and thats the reason to keep it going.