Hi, I accidentally broke a small Pseudotrichia rubiginosa shell - and found this pupa inside! The shell was found in February, in forest, NE Hungary. Pupa around 3,5 mm.
No problems to rear flies from pupae. As a rule it is enough to put it inside some moisten (but not wet) moss or paper or moist sand + moss or paper and close with cup admitting air circulation. If you wait for some time I think it will emerge. Sometimes it may be useful to put in in some warm place.
With best wishes.