Yes the online information says it CAN be done, but immigration will pull every trick out of the hat to make it as difficult as possible to do so. They don’t want you to do it. They want you to bounce.
As I said some have managed it but I would hazard a guess that out of those that have most won’t bother again.
Not really sure what you’re asking here. If you have an extension of stay based on a particular reason and that reason finishes then the extension of stay finishes that day. Marriage, Work, etc.
The only difference is that if it’s based on marriage and the spouse dies then you can stay until your extension finishes. You’d then either need to leave or switch to another reason for an extension.