I've experimented a bit.
If the DB is not available the *-ds will not be deployed.
The EJB2 persistence jar depend on the DS and is also not deployed.
If the DB is available again --> NOTHING happen
If I touch the *-ds.xml afterwards, the DS and the EJB.jar is started.
I'm don't know whether there is an option to force that the DS check the DB-connection periodicaly :(