From what i can remember from my limited knowledge what happens there, the mission ends because its end goal was reached.

The missions goal is to save Raz by getting an allied character to the area behind him. So the idea is to use Riley to make Raz man up and save himself with some explosive encouragement. So you use Riley to shoot Raz few times so that he ragdolls and/or stands up in the end zone and finishes the mission. The RNG in this come from where Riley's shots land, wacky ragdoll physics and where Raz decides to stand up.

Somebody else probably knows better but i do hope this helped you to understand this atleast a bit more.

You can create a new user on switch to get a new save slot so that you don't need to delete your save where you have 100% the DLC. Locking the DLC-items means to "lock" them in the weapons list in shop, smith or equipt screans by pressing some buttom whule hovering over them. Locking stops you from selling or fusing the weapon by mistake. You aren't required to do it but it is recommended so that you don't invalide your run by mistake. Only way to fully disable the DLC would be to factory reset your switch and then not download the DLC. Because of that if you want to do the NG run using DLC-items go for it, we in the mod team will then make sure there is a valid category for it. If you decide to do the run under current rules, we in mod team probably will compensate sometime for DLC related time loss.

So if i leave a comment, nobody is going to find it?

Audio isn't required for a run but it is recomended to have audio. ILs require video that show difficulty and full run of the level so a picture of a end screan isn't enough.

There is a dev intended skip in 'Road to ancient lab' where you kill the guardian when it appears and there is also few cutscene skips: in 'Daruk, The goron hero' and 'Calamity Strikes' for example, i'm not sure if cutscene skips are used in any%.

People in this games speedrun discord server can probably help you more so you could ask more about this there.

I'm pretty sure it is allowed as there is an option to add discord servers link to the main list of things (the list with leaderboard, guides and forum) in here

Using slide oob on the spot that is in that twitch clip and then walking left allows you to enter load zone that enters upper underground hall

I would also suggest Sisters ending - Easy/Normal/Hard as i feel like sisters ending does do enough stuff to differentiate from All Bosses