Will humanity's knowledge be lost if all computers are wiped out by war?
Or is there some sort of emergency hard copy procedure that would take place?
How much knowledge in indigenous North American cultures (for example, because it's what I'm more-familiar with) has been lost in the ongoing Euro-colonial steamroller? That knowledge is not gone, but the oral and practical traditions have been significantly stressed. If we care about existing for another, say, fifty thousand years it seems likely the knowledge, skills, and abilities from the last fifty thousand will be useful, along with the wisdom to set and respect some limits.
No, there are books and there's the knowledge people have in their heads. The bigger danger is the declining of society over a few hundred years. If there is no preparations for it. We could see a loss of knowledge. We could have a situation where knowledge is locked in machines and books without humanity being able to access it.
Nah. Tons of knowledge is still in books, and Wikipedia has been backed up enough that we shouldn't lose that.
Bigger concern is a massive EMP (like from the sun) could wreck electronics and our power grid. Our society might not survive that.
This doesn't fully answer the question but I believe that the total contents of GitHub was archived in the Arctic or something by Microsoft a few years back. That's something.