It won't be very good for Real Madrid if they become out of the Copa del Rey as well. Because they have already lost most of their chance to win the La Liga title. If they get eliminated by Barcelona in the Copa del Rey as well they will have only the Champions League left. Finishing the season without a title would be really bad for Real Madrid.
Barcelona can really push them out of the Copa del Rey by the way. Because they already beat them in the Santiago Bernabeu in the first leg. I think they would finish the incomplete job.
It looks like Barcelona will be able to play even better in the second leg of the semi-finals in the Copa Del Rey. even so Barcelona only beat Real Madrid by a narrow score in the first leg, namely 1-0. so that in the second leg later Real Madrid still have a wide enough chance if they can be more productive in scoring goals. but the problem is Barcelona's defense I think is very solid at the moment. so that for Barcelona even a draw was enough to qualify for the final. and maybe Barcelona will actually score more goals in the second leg later because Barcelona will certainly have higher motivation because they are playing at home.