If you do not want to use WM anymore, then there is basically not much more needed than removing the assignment of the warehouse from plant/storage location combination.
WM is only triggered if you post a movement with a storage location which has WM assignment. If the assignment is gone, then you work solely in IM, no extra customizing needed for this.
However, it is too blue-eyed to do nothing more than just removing the assignment.
if you have open deliveries then they expect picking/confirmation of picking in WM. Those deliveries have to be completed or removed before you remove the link.
Further you have to think about the data left in WM. If you physically close a warehouse, then you may move everything to some other place. If everything was well maintained, then there should not be any open TR, TO or PCN when the last piece has left.
So you could consider archiving this data to get a clean environment, which is anyway beneficial, as such things will certainly come up again later, e.g. when you get an archiving project and want archive materials
If you are just closing WM because of a big mess, then you are usually not able to clean the data, otherwise you would have been able to teach the users and to keep WM alive.
Removing the link will just leave the garbage (unprocessed documents and even stocks) in the table space and may disturb you later from doing some archiving work.
In any case you should set a deletion indicator in all materials for this warehouse, easiest done with MM17 at table MLGN.
