Youngstown is pretty isolated in the USHL. They're closest rival is the USNTDP and they're about 370 km's away. Next closest after that - Muskegon and Chicago - are both 640 to 680 km's away.
Youngstown -> Erie
160 km
Youngstown -> Niagara
360 km
Youngstown -> Hamilton
410 km
Youngstown -> Windsor
380 km
Youngstown -> Flint
460 km
Youngstown -> Saginaw
505 km
Considering the pitiful attendance Youngstown has in the USHL, they would never survive in the OHL. You're more likely to see the USHL grow around the Youngstown "island." The USHL could promote Johnstown, then look at Dayton, Akron, Canton, Huntington WV, Trenton, Atlantic City, Danbury, Wheeling (if they should lose the ECHL), Elmira (as with Wheeling), and perhaps even Pittsburgh and Philadelphia in the same way that the WHL works with Vancouver, Edmonton and Calgary). If the new ownership in Erie decides to head North, the USHL would also be a good bet there.
As for the OHL moving south, I would look at Buffalo first and foremost. It's a shame the Harborcenter isn't bigger, but I wonder if Pegula had interest if he could simply have them play in the Sabres' arena and just use the lower bowl. As mentioned above, it works for big markets in the WHL.