He won't be sacked for this, nor should he be.
He failed road side, went back to the station for the super sal, passed that. ThereforE the police say he is fit to drive and by law he has done nothing wrong. Now he will have a sample sent to the lab. If he passes then sweet all good but if he fails then he is in shit and then and only then can you punish him re the drug and alcohol tests.
It would be a million to one he comes back positive for the gear. Especially as the kit picks up meth, weed or pingers only.