A card will always go to its Owner's graveyard, the owner being the person who started the duel with that card in his deck. So if the opponent takes control of one of your monsters, then it still goes to your graveyard when destroyed.
XYZ material monsters no longer count as being monsters on the field, any equip cards will fall off, they will go to the graveyard. Ekibyo Drakmord can only return to hand when it destroys the monster it equips. In this case it will simply go to the graveyard and can't return, it went there as its equip target became an invalid one.
Flint is sent to the graveyard
When a non-effect monster destroys another monster the destroyed monster is sent to the grave, unless there is another card on the field which changes where destroyed monsters go. Depending on the effect of the monster that destroyed them they are either sent to the Graveyard, are banished, return to the owners hand, or can be summoned on the opponents side of the field. Some cards can even be saved from the grave by their own effect and are then either re-summoned or go to spell/trap zone. Spell/trap cards can also determine where they go, as they can change it so that any destroyed monster is banished instead of being sent to the graveyard.
If an equipped monster finds itself no longer equipped to a monster for any reason, then it is sent to the graveyard.
Any movement of a card from another zone to the graveyard, is a send. 'Tribute', 'Discard' and 'Destroy' are specific kinds of send. XYZ material is 'sent to the graveyard' if the XYZ monster that overlays them is destroyed, removed from play, returned to the Extra Deck, etc.One exception is cards that have been removed from the game. They can be 'returned' to the graveyard, but not 'sent' from there.
No, there is nothing that can do that.
No, there's absolutely nothing of the sort. The monster goes to the graveyard, just like any other tributed monster.
Yes you can, as long as the Stardust was originally summoned by Synchro Summon and not by Starlight Road (Starlight Road does not summon it 'properly', and the Stardust Dragon summoned by it cannot be summoned back from the graveyard should it be sent there).
De-Synchron is not a real card
No, you do not 'tribute' the Synchro Material for a Synchro Summon. They are sent to the graveyard, not tributed. You can tribute an opponents synchro monster for "Assault Mode Activate!" to summon the assault mode monster from your deck.
If it is originally in your hand, then yes, you may send the Machina Fortress in hand as well as one other monster, and then special summon that same Machina Fortress from the graveyard.
The monster will always return to its owner's Graveyard. Incidentally, if the effect of the destroyed monster activates while it is still on the field, you will be able to use it; however, if the effect activates in the Graveyard, the card's owner will control the effect.
Yes.
In the graveyard
Yes you can
XYZ material monsters no longer count as being monsters on the field, any equip cards will fall off, they will go to the graveyard. Ekibyo Drakmord can only return to hand when it destroys the monster it equips. In this case it will simply go to the graveyard and can't return, it went there as its equip target became an invalid one.
Flint is sent to the graveyard