WEll there are 3 major franchises that i will include here and that is

Mac

Windows

Linux

now the debate is which one will last, i think that windows will most likely last the longes although they wont be top dog by such a gap. Mac is slowly gunna rise with thier compatibiltiy and ablility to make things INCREDABLEY easy to use and convientent

(dont mind me spellin)

Linux will always survive as when some1 needs a server to be secure and safe, never crash. This is where you look for linux windows and mac sucks for this...