CiviCase case closed and remove remaining activities
I'm not sure what you're looking for other than to just confirm the behavior that you're seeing, in which case the answer is "no" and "no". i.e. it does not currently do those things.

Could it work differently? Probably. The history is that when the feature was first added it was left pretty basic because while there were lots of ideas tossed around, the feature itself and nailing down the full set of use-cases wasn't a priority, and it wasn't desired to spend time/money on things where it wasn't clear yet if they'd be used or not.

One way to implement your workflow is to have activities 3 and 4 be configured as part of another timeline/sequence, and then after the staffer does 2, if the person is interested the staffer chooses "Add timeline" and picks the other timeline/sequence.