Well the simple fact is that if your regulation fails the opto will blow up if that's what you're wondering. If the regulation works its all good...
It's wise to have some sort of failsafe since the nature of negative feedback is that any failure causes the output to pin to the positive rail...however the reality is that many circuits don't have such a protection.
Am I correct that this is an on/off type control scheme? If that's the case you could replace the resistor with a current regulator/limit set to 10-20mA. That would also 'sharpen' the turn on and therefore regulation. I like this depletion mosfet current limit circuit:
https://ixapps.ixys.com/DataSheet/98704.pdf