If they did just that, stayed in their own newly claimed borders, did not venture outside those borders, and swore off external violence, and sought to live in the Dark Ages that would be fine. If they then compounded that by refusing sanctuary to any person or group that espoused Jihad against anyone or any other nation then that would be fine.
Now do you believe in the Tooth Fairy?
Because that is the kind of thinking it would take for One to actually believe that is possible or likely.