If spirit monster's effect is negated for 1 turn, does it return to hand by end phase?

Question

So let's say player A summoned Dark Dust Spirit, then:

Case 1: Player B activates Forbidden Chalice on Dark Dust Spirit so its effect is negated until end phase. Does it return to hand by end phase?

Case 2: Player B activates Skill Drain on Dark Dust Spirit so its effect is negated. Then on next turn (player B's turn), Skill Drain was destroyed. Will Dark Dust Spirit stay on the field for all the upcoming turns?

Dark Dust Spirit:

Cannot be Special Summoned. During the End Phase of the turn this card is Normal Summoned or flipped face-up: Return it to the hand. When this card is Normal Summoned or flipped face-up: Destroy all other face-up monsters on the field.

Forbidden Chalice:

Target 1 face-up monster on the field; until the end of this turn, that target gains 400 ATK, but its effects are negated.

Skill Drain:

Activate by paying 1000 Life Points. The effects of all face-up monsters on the field are negated while those monsters are face-up on the field (but their effects can still be activated).

Answer 1

No, It Does Not Return To Hand

The effect written on Spirit monsters is an activated effect, which activates during the End Phase. When a monster's effect is negated "until the end of this turn," this applies throughout the End Phase; i.e, the effect(s) will be negated until the beginning of the next player's turn.

Case 1:

Forbidden Chalice negates the effects of Dark Dust Spirit until the end of the turn. During the End Phase, the effect of Dark Dust Spirit will activate, but be negated by Chalice - Dark Dusk Spirit remains on the field.

Case 2:

The effect of Dark Dust Spirit activates during the End Phase. Because Dark Dust Spirit is a face-up monster on the field, that effect will be negated by Skill Drain - Dark Dust Spirit remains on the field.

It Will Remain On The Field Each Turn

The effect's activation timing is "During the End Phase of the turn this card is Normal Summoned or flipped face-up:". After that initial turn of its summon has passed, the effect will not activate again on any subsequent turn - unless, of course, it incidentally happens to be flipped face-down and back up again.