Bright day
I do know very little about warfare, but I do have some beliefs.
Well IF there is world-scale conventional conflict, I doubt somebody would be the one side to start using missiles with nuclear payload (of course you cannout tell if it is nuclear or conventional warhead), plus in not-so-distant future we could improve energy effectivness of lasers and/or finally get knack for rail-guns, both of which ,with advanced computing technology and orbital surveilllence systems, could lead to missiles (and airplanes) being destroyed shortly after takeoff. Further strategic bombarding goes after strategic targets (

), civilian population nowadays is not one of these nowadays (though often targets are located in or near population centers), more alive but desolate civilians may hinder your enemy ahe needs to cater to them. Though civilians
may be used for draft, your first strike already destroyed large numbers of industry, material stokpiles and eliminated enemy's energy grid, communications and leadership. And if not what the hell are you doing starting this war? My two cents on subject of WWIII.
After it, well in case of one's side victory, well that is up to them. In case of mutual and global-wide collapse (even you Solomon Islanders!), we can expect socio-economic changes to come rapidly, as far as I can understand, our society caneven devolve. I doubt we would lose much in terms of already widely known technology, one would have to eliminate each and every one of tens thousands learning institutions around the globe for that. We will probably see less aplied technology as we would be short on energy and materials- which very well should lead to famine and outbreaks of epidemic diseases. Oh and after that we will have a even greater lack of labour. But what thatt could leat to most of us cannot even speculate.
Addendum: If somebody feels like I am cutting meter high letters into rock, please understand that this very subjective non-profesional view, based only on the few bits of wits (

) I so far managed to, somehow, acquire.
EDIT#1: changed "opininons" in the second sentence second row to "beliefs".