Jesse use to do the exact same thing. He hated tummy time so the minute he'd roll over, he'd scream cos he couldnt get back. It was frustraiting for both of us but he too learnt to roll back (it wont be too long!). I would get down with him and talk to him while on his tummy for as long as it would last (about 1 minute!). Until he learnt to roll back i just tried to find things for him to do on his back so he wouldnt wanna roll over, like baby gyms etc. But to answer your question, if he was crying, no i wouldnt leave him there, id roll him back or pick him up. Whether its the right thing to do or no, i didnt care, i didnt like hearing my baby cry.

Oh dont worry hun.. once they start to become mobile they are more easily amused i think... jesse can play with things by himself now.. but there have been a few head bangs from trying to stand up and falling down! Comes with the territory i think