Well he wouldn't want the bad people, and there are only a handful good ones around, so I imagine he would tell those to go forth and procreate. God would leave them here to get the job done. So I guess my answer is zero.
From a Christian perspective, He would definitely leave behind all of those who don't love everyone unconditionally. Do you have hatred towards a neighbor? Don't pack your bags yet. Do you have trouble loving liberals or conservatives? You're sticking around too. Do you find yourself thinking that other cultures or religions are worse than you? Then hand your ticket to somebody else - you won't be needing it. If God were to come today, reality is that the only ones on the bus will be those who have learned to love each other as Jesus loves us. The rest aren't prepared to unite as one with Christ.