The Sim only accounts for the phone number attached to the persons cell service, possibly some of the telephone/SMS contacts (a feature rarely used since pre-android/iphone days) and if the data plan bill has been paid (if it's active or shut-off).

Everything else is entirely independent. Signal might lock itself from view detecting a phone number change but all the other social media won't even care.

The virtual SD post I'm going to assume is referring to how Android doesn't see internal storage any differently from old phones that had only an SD card. What they might have meant really is that pixel phones encrypt the internal storage by default and if the phone powered off all the way will NOT automatically launch any social media applications until the first un-lock of the screen.

That said Google always makes exceptions to their own apps and likely Play Services will ping back the GPS and sync basic notifications anyways the moment it's on the internet.

If the phone had never turned off then putting in the sim even without unlocking everything in the background will still be running and able to sync.