Can I get a Minecraft server level from a client?
Solution 1:
No, you cannot get it back from client. Because you never gave the whole level to the client. You did open to LAN, which sends only required chunks to client's ram.
The only option you have is some recovery software. there are bunch of them.
NOTE:- If you are running a server(open to LAN as well) then make backup every day. Use a batch file to do so.