It does not need to be connected at all times. If you set Origin to be in offline mode (or tweak the "In Game" settings), it just needs to be running, not connected. Do the same with the Sims 4 "Other" Settings (the ones that relate to being online and using your information) and that's it.

Yes, I was stupid. I did make a backup copy, but I think I eventually deleted it...

If anyone can help, I would really appreciate it.

Could anyone share their original TS3EP03.exe and TSLHost.dll, so I can update to the latest patch, please? I use an arr'ed copy of TS3 and lost the original files :S

Thank you.