Depends on:
how out of date it is - 1-2 months should be OK, 2 years?/
How it has been stored.. if cool dark ,probably OK, if hot and in sunlight, probably not..
Some leakage of thymol vapour will happen over time..
And is it worth the risk? Downside either kill bees or ineffective. Upside save cost of ?( not £100s surely
Apiguard is poor enough to start with, IMO. Using it when seriously past its use by date could be a disaster for the bees - especially in the hands of someone who simply follows the instructions but does not do the necessary checks on efficacy.