Well, that all depends on if your chamber face is dented from the firing pin. You'll hve to inspect for this and see. But, I suspect your breech face is fine since your pistol would have had to be disassembled for the Firing Pin Stop to fall out.
As far as being unsafe the answer is- yes, for now. The good news is; Ruger will send you a new Rebound Spring and Rebound Spring Suppport if you contact them, for free.
The new spring will go into the narrow end of the Rebound Spring Support and the assembled rebound group fits under the Firing Pin with the spring end against the flat part of the firing pin, to force it back when the hammer isn't striking the pin.