A client has reached out to me re his v10 site where I have access to his hosting (via ftp) but I didn't build it and hence don't have the source code for the project. He wants me to update it to the latest patch released today but without the source, obviously we can't nuget update it. Is there a way around this or will I need to get him to provide the source project files so we can do in the usual way? In the old v7v8 days, we could just copy the new binaries etc over so was easy in this instance.

The only thing that needs changing is the versions in the .csproj files and then they can deploy as per how they deploy. You can't just upload dlls, it might work but once the project gets deployed again, the old dlls will be put back.

I did mention that to them but they no longer have any developer and the code is with the old dev that wont release it. They were hoping to just copy over but such is life!

Depended on the rules on the country, and the agreement of course, the company who hired the developer is the owner of the source code.. Could be worth it to check if it's legal and force him to release it ?