If they are from the common German cockroach and were still attached, they will probably dry out and won't hatch. If they were dropped naturally before you killed the roach, they will likely hatch within 24 hours.

"If the egg cases are from a German cockroach (which is by far the most common cockroach found in apartments), they have most likely either already hatched or are probably not viable. The German cockroach female is unusual in that she carries her egg case protruding from her abdomen for about 3 weeks, until just before it is ready to hatch. About 24 hours before hatching, she places it in a secure place. If she drops the egg case before it is ready to hatch, it usually dries out and the cockroach embryos do not complete development.

There are three possibilities:

?The egg cases have already hatched.

?The egg cases are no longer viable and will not hatch.

?The egg cases were very recently deposited by a cockroach and could hatch very shortly."

http://www.colonialpest.com/can-that-coc...

Give us some more information.