Non [Death from Above]  Talent combinations:

The gameplay changes abit when not playing with  [Death from Above].

Pre pull and Opener:

Be sure that you have  [Lavish Suramar Feast],  [Defiled Augment Rune] and  [Flask of the Seventh Demon]  up when the pull timer starts.
Use  [Tricks of the Trade]  on the main tank.
Use  [Potion of Prolonged Power]  with 1 second left on pull timer. 
Use  [Shadow Blades]  on pull. 

If you select [Marked for Death], you will have an additional ability to use before the pull.
This is due to the fact that combo points start decreasing after 20 seconds in an interval of 1 CP every 10 seconds.
The changes made the [Marked for Death] cooldown 40 seconds,
so you will always be guaranteed at least 4 combo points at the pull.
We always start with [Shadowstrike] which means we gain an additional cast of [Marked for Death] during the opener in the best case scenario
Opener(without  [The First of the Dead] ):

Opener(with  [The First of the Dead] ):

[Nightblade]  will be used at 3 CP during the opener when not using   [Marked for Death].

Rotation:

The main change comes from the loss of the [Death from Above]  interaction wich gives us more options to vary our  [Shadow Dance]  and  [Vanish]  usage.

We use  [Symbols of Death] on cooldown.

[Shadow Dance]  is used with 4 or less combo points during  [Symbols of Death] or when  [Symbols of Death]  cooldown is higher then 12 seconds (15 with T20 4p and  [Dark Shadow] talent). You will always cast  [Shadowstrike]  if possible and spend your combo points with  [Eviscerate]  when you are at or above 5.   [Shadow Dance]  is also used when you are about to cap on  [Shadow Dance]  charges. [Shadow Dance]  is also not used during  the  [The First of the Dead] buff. Keep in mind to not cast  [Shadow Dance]  if you would need to refresh  [Nightblade]  during the duration.

[Vanish]  is used during  [Symbols of Death]  folowed by one  [Shadowstrike] . [Shadow Dance] is aligned to it if you wear [Mantle of the Master Assassin].

[Marked for Death]  is used on cooldown but not during  [Vanish],  [Stealth], [Subterfuge] (if talented) or  [Shadow Dance].  you can delay it slightly on add fights and abuse the reset on dying adds.

[Backstab]  is our main combo builder that gets replaced by  [Gloomblade]  if talented.

[Nightblade]  is best cycled in a way where you don't need to refresh it during symbols while still playing around   [Finality]  and Pandemic. 

Pandemic timers are:

  - without T19 2p 
4.8 seconds with 5 combo points
 5.4 seconds with 6 combo points (DS) 

- with T19 2p 
7.8 seconds with 5 combo points   
9 seconds with 6 combo points (DS) 

The usual rotation is: 

start -> apply   [Nightblade]-> refresh   [Nightblade]  with the highest possible pandemic time -> let it run to the last tick -> start

However we can break this circle to meet the requirement to have the duration of   [Symbols of Death]  covered by   [Nightblade]. We refresh  [Nightblade]  with 5 combo points up to 5 seconds before   [Symbols of Death]  comes up or 6 seconds with 6 combo points.  

[Eviscerate]  and  [Nightblade]  are always used at 5 or 6 combo points..

[Goremaw's Bite]  is used with 2 or less combo points and 50 or less energy (90 with  [Vigor]) and not during  [Shadow Dance],  [Stealth],  [Vanish]  or  [Subterfuge].

[Shuriken Toss]  is only used when you are out of range of the boss, need to dump energy, and have no other options..

[Shadow Blades]  is used on cooldown.

Multi target:

[Shuriken Storm]  replaces  [Backstab]  with 2 or more targets.3 or more if [Master of Subtlety] or [Symbols of Death] is up.
[Shuriken Storm]  replaces  [Shadowstrike]  with 3 or more targets during  [Vanish],  [Stealth], [Subterfuge]  or  [Shadow Dance].

[Nightblade]  is applied to all targets. 
Only apply to additional targets if they survive for a minimum fo 12 seconds.
Keep in mind that using  [Nightblade]  on multiple targets results in primary target damage loss.

[Eviscerate]  can be used on 4 combo points with 4 targets.

[The Dreadlord's Deceit]  doesen't change the multi taget rotation. If you use it on single target fights use   [Shuriken Storm]  as a combo builder if you are on 29 or more stacks during [Shadow Dance]. 

Trinkets:

When using multiple On-Use trinkets, the use of one trinket will trigger a 10 second cooldown on the second trinket which is something to keep in mind.
If you use  [Specter of Betrayal]  in combination with another On-Use trinket, prioritize it over your other trinket and most likely use the second trinket on as soon as the cooldown finishes.

Some trinkets have special use conditions, the most popular of which I have listed here:

[Specter of Betrayal]  - Use when in   [Shadow Dance]  during  [Symbols of Death]. You can macro it to  [Shadow Dance]  if you want. Just keep in mind to properly position yourself when using the trinket. 

[Umbral Moonglaives]  - Use it when  [Shadow Dance] and  [Symbols of Death]  are up. You can adjust the use in multi target situations to use it with  [Symbols of Death]  and get the explosion during  [Shadow Dance] (if possible).

[Vial of Ceaseless Toxins]  - Use it with  [Shadow Dance]  and  [Symbols of Death]  up. You can adjust the use to abuse the reset in add fights.

Mythic plus: Switching trinkets in mythic plus dungeons is common practice. If you switch a trinket it will trigger a 30 second cooldown on the newly equipped trinket. You can use this time to prepare for specific mob groups/pulls.

Optimization:

[Shadow Techniques]  - The proc can also be used during  [Shadow Dance]  when on 4 cp but i don't recommend it becouse of the tight time window of  [Shadow Dance]  that can result in the loss of 1 ability cast during the buff.

Energy Pooling:
Pooling became less important due to the increse of energy gain from  [Symbols of Death]  and  [Shadow Techniques]  as well as the chance to proc   [Energetic Stabbing]  on  [Backstab].

Certain abilities will still benefit from Pooling.

[Vanish]  you want to use it with 55+ energy.

[Shadow Dance]  - you want to be at an energy level that allows you to perform 4 abilities during the buff.
 An energy level of 70-75 is sufficient in this situation. I made a calculation about this. You can take a look at:  Calculation. 

Utility Cooldowns: 
[Cloak of Shadows] - is mainly used to get higher uptimes during boss fights by avoiding damage from boss mechanics if possible. Certain boss fights will require you to use the ability to soak abilities. 

[Sprint]/  [Shadowstep]  - is mainly used to get higher uptimes on the boss,  [Shadowstep]  can also be used on bosses, adds or friendly players to avoid knockbacks. 

[Feint]  - is only used if needed for a certain boss mechanic as it consumes quite alot of energy.

[Crimson Vial]  - only used if you would otherwise die. There should usually be no reason in a raid enviroment to use it.

Final Words:

If you want me to add anything to the guide or have questions you can contact me via Discord or PM me. Everyone makes mistakes, so if you find a mistake feel free to contact me. My Discord tag is fuu#7750.