I think the solution to this is really never as difficult as very first appears. (i am assuming you are not puzzled in what takes place when a trampling, lifelink creature without two fold hit gets blocked.) It all hinges off the next easy (ish) guideline for resolving trample:
702.18c If an assaulting animal with trample is obstructed, but there are not any animals blocking it whenever damage is assigned, all its harm is assigned on player or planeswalker it really is assaulting.
Recall that a dual striker deals harm both in initial attack fight damage action, while the typical combat damage step. Now, it may perfectly be your blocking creature was dealt deadly damage in the first hit combat harm (many trample damage may also have carried to the defending player). In this situation, the blocker is within the graveyard once associated with normal combat harm step, but, crucially, it doesn't imply that this harm action doesn't take place.
If dual striker don't have trample, then the regular fight harm action could be fundamentally irrelevant: the dual striker however counts as having been blocked, and blocked animals deal no damage to the protecting player. ETA: also, the lifeless blocker isn't any longer in combat to just take more harm (which might be essential if the attacking creature had lifelink). But tramplers can deal injury to defending players; actually, any level of harm that is not "absorbed" by a defending creature. Which in this case is all the damage dealt in the typical combat damage step, while the defending creature is not around to soak up everything. As suggested by Rule 702.18c.
The lifelink is a little of a part issue, I feel: it doesn't change any such thing in regards to the double hit or trample. It simply provides the same quantity of life into the animal's controller to the harm that creature deals, in either combat damage action, and whether that damage is always to a blocking creature or a defending player!