On the 'Indian Muslims' or as 'Mohajirs' or 'Urdu Speakers' as they are called : Should you wish to, I could help identify no less than 5-10 of them on this very forum and you can ask them these questions yourselves; or better yet PM Bilalhaider or Pakistanisage - both are Pakistanis born of parents who immigrated to what would become 'Pakistan' ! But if I might add some anecdotal evidence - I haven't come across a single one of these 'Urdu Speakers' who feel that they made a mistake coming to Pakistan and I've had the good fortune of having met many including one who married into our family (my cousin's wife !). Also if, Kashmiri Muslims, can be called 'Immigrants' as well then I've got a few relatives on my Dad's side (hes an ethnic Kashmiri !) who immigrated to Pakistan and in particular Sialkot and later Lahore, from Jammu; some of them even lost their loved ones and naturally they don't think that they made a mistake !
So dear friend...I do implore you to come to Pakistan, visit these communities for yourselves, interact with the common Pakistani yourselves and then don't be surprised if it turns out that the realities of Pakistan, however grim they maybe, are far from the ones that have been sketched out in the media ! Indian Muslims who choose Pakistan are as Pakistanis as the rest of us if not more because of the amount of sacrifices they made and they are treated as such ! However don't confuse our contempt for, or so it is perceived, the militant organization MQM as our contempt for the 'Urdu Speakers/Mohajir Community !'
Had Pakistan not let them down so terribly more would want to come back to 'Pakistan' as they should have been in the '70s, the '80s and throughout the '90s !
I doubt if the Biharis ever numbered in the 'Millions' in BD to begin with ! A million..yes, a couple million - probably not !