There are more or less 81 words of power in the game, but you don't need the greybeards to find them. It will be more difficult to find them, sure but joining the blades is a way to pass time. You will lose the privilege of speaking to the greybeards about the locations of words of power after killing Paarthurnax.
Like the quest page says once they bought it up the Blades won't have anything to do with you until he's dead, and the Graybeards won't have anything to do with you after you kill him. The Greybeards quest Find the Word of Power is the same as Find the Source of Power but Meditations on the Words of Power can only done with Paarthurnax.
Sometime after defeating Alduin if you haven't killed him the quest will disappear for your journal, not really sure when but it's happened to me several times.
There are a lots of threads on whether or not to kill Paarthurnax.
For word walls reload and try again or save by the wall and quit out of the game then reload. You could also try leave the area for bit then going back trying and again. But check the wiki pages bugs list for that shout and the location as some do have their own bugs. Also you can occasionally be sent after words you already learnt.
For me killing Delphine instead can be better. That woman after the "Parthurnaax" doesn't give any more quests, no more dungeons to clear for her, so she's useless, just walking around and helping nothing. Greybeards are more helpful as they teach more than the Blades and of course Parthurnaax helps you with meditating. So no, don't kill him, kill Delphine instead, even with commands, as she's more annoying than Lydia.