The garage will replace the pedal, it's quicker for them and doesn't involve them in any issues about making parts non-standard.
A good garage will quote you for removing the pedal, welding it up and replacing with a new clip, but it is almost certain to cost more than a pedal replacement, as it will take more of their time.
The plastic clip is there to center the master cylinder pushrod in the little box on the pedal
I don't know if new pedals have been modified to fix this failure mode.
Once the pedal has been fixed, keep an eye on hydraulic fluid level. Sometimes that master cylinder seals can be damaged by the sudden release of the master cylinder piston, which gets driven to the end of the cylinder, where it wouldn't normally go. The damaged seal leaks hydraulic fluid out of the end, but it disappears straight under the carpet and isn't immediately obvious inside the car. The only cure is master cylinder replacement, as the seals can't be got separately.
If you can see hydraulic fluid leaking from the cylinder now, then best to get it replaced at the same time as the pedal.
This happened to me in my old
Ibiza.