Sensei's Divining top

[Offler]

I was just thinking about this card.

For some months i know that it is terribly hard to destroy it, but i was unable to resolve one problem.

Situation A:
SDT is on the table.
Opponent will cast instant "destroy artifact" spell without "Split second"
I will Tap the Top and it is saved. Pretty simple.

Situation B:
SDT is on the table.
Opponent will cast instant "destroy artifact" spell WITH "Split second".
I cannot do anything with it. Again i have no problem with it.

Situation C:
SDT is on the table.
I am tapping the TOP.
Opponent will cast instant "Destroy artifact" spell without/WITH "Split second".
Top is destroyed, but what happens upon resolution of its Ability?

Getting the Top off the table is not part of cost, but part of effect. If the TOP should target itself it should be easy to understand that its own ability has no legal target therefore it will fizzle completely (no draw, no SDT). But... it does not target, so i am very unsure + possible situation when two tops are on the table...(Can i force my opponent to put its own top on top of library, while mine stays in game?)

Maybe i am just thinking too much about the card, but i was unable to find any clue to this...

Edit: moNths, not moths :D

[Otter]

Situation C you attempt to resolve as much of Top as you can. The put on top of library can't be done, so you move on and just draw a card.