Nuclear never was a very large part of the German grid and currently the nuclear capacity is like 10% of the daily peak load. So while shutting down the nuclear power plants does make a carbon-free grid a bit more difficult, it won't make a huge difference. Most nuclear power plants would have been scheduled for decommission in the late 20ies or early 30is at maximum anyway.
The existing plants are getting older, we still don't have any permanent storage nor is any in sight. Finally, it was already agreed in the early 2000s, that Germany should phase out nuclear energy and an end date was set for the mid-20ies. The Fukushima disaster only accellerated the plans for phasing out nuclear.
The energy is supposed to come from reneweable sources. Just from 2018 to 2019 their contribution to the grid jumped from 40 to over 45% due to coal becoming less attractive. There are no plants to net import energy into Germany. Up today we have been net exporters of electric energy. Of course, going forward the European grid will play a larger role, as it is a great way of balancing local fluctuations in wind and sun.
