Take it back to the shop and tell the manager you want a new valve or a new tank! I manage a PB Pro Shop and this kind of thing is completely unacceptable. This idiot should have never been holding the tank upside down. The valve is brass and if you try to bend it back that bent piece WILL break off. To answer your question, yes, the o-ring will probably seal. But as time goes by and with every time you screw/unscrew the tank, the crack will get weaker and weaker. In a year or two it will crack off and you'll likely be SOL. I sell 20oz tanks to aquarists for $20 filled. So it's no big deal for them to replace a $6 valve. Next you'll tell me they charged you for the fill! Lol! PM me if you have trouble with them.
Nikon Pimp #084
"The legal quarter of tight lipped men, push for order, then repeat again." KTP