What is even going on? SPOILERS

Storywise that was the perfect outcome, otherwise Hyung Jo would've been pointless, his arc would've been completely useless, and it would have had no impact on the other characters and the story whatsoever.

Hyung Jo might indeed reset again to undo his mistake, others might survive but he'll probably suffer for life.

Since we're entering the last episodes I'm going to sum up everything for those who are completely lost on the story. 

Huge spoiler alert for new viewers, only read this if you're up to date with the drama!!

It all starts with lady Lee Shin. She loses her daughter and somehow gains the ability to reset (likely related to the mysterious professor) but she cannot save her ill daughter somehow. She resets multiple times but eventually decides to use other humans to experiment on fate. 

Enter timeline version 1. In this 2019-2020 timeline everyone in the group-reset is killed by serial killer Sun Ho who is the detective-partner of Hyung Jo. He collects mementos from people and puts them on display in a room. 

Lee Shin resets and starts timeline version 2. Here she directs a hateful dying criminal to kill Sun Ho so that every group-resetter is saved. She convinces the criminal to do this by telling him that it would make detective Hyung Jo suffer. Webtoon creator Ga Hyun (creator of ''Hidden Killer'') becomes paralyzed in this timeline and detective Hyung Jo is depressed because Sun Ho died. Lee Shin reaches out to all previous victims of Sun Ho and convinces them that they can do a reset of a year. Everyone has their own reasons to reset and Lee Shin knows that Hyung Jo will save Sun Ho in the new timeline. All but 1 person agree to go and they plunge to their deaths in a car since dying is required for a reset. 

Enter timeline version 3. They wake up in their bodies a year earlier. Every resetter does the things they wanted to achieve but 1 resetter died immediately thanks to a carcrash. Hyung Jo goes to arrest the dying criminal and saves Sun Ho's life because he thinks his friend is a good person. From this point on resetters start dying one by one thanks to Sun Ho and Lee Shin knows their predicted time of death. Lee Shin sends them flowers before death to try and warn them to change their fate themselves. The gamer-resetter contantly tries to test how to find out who dies next. Suspicion arises within the reset-group since some reset-people secretly meet with Lee Shin and some get into fights with each other. The person who chose not to reset dies in this timeline by explosion. Sun Ho gets injured chasing a gangster-resetter and the killings stop for 7 months. 

After that 7 month timeskip an uninvolved person is killed from the same company as the resetter who died during the reset. The detective wonders if this is connected to them since a new person died in the place of a resetter. It's really just the timeline version 1 murder-plans of Sun Ho that are occuring. Sun Ho finds out about the resetters and he wants to fulfill his fate from the original timeline so he follows the list of names from detective Hyung Jo. Resetters start to die again after this. Ga Hyun figures out the killer has to be involved with the police. Gangster-resetter is killed by Sun Ho but gamer-resetter thinks it's detective Hyung Jo that killed gangster-resetter. A tape is released that has gangster-resetter whispering ''detective'' before dying and detective Hyung Jo becomes a key suspect. Meanwhile webtoon artist Ga Hyun gets kidnapped by her unsatisfied webtoon-assistant and saved by Hyung Jo and Sun Ho.

Gamer-resetter finds out the truth of the real serial killer and he dies. Detective Hyung Jo is tricked into going to his dead body by Sun Ho and caught by the police. He runs away and is sheltered by Sun Ho (since he can use him as a decoy suspect). Ga Hyun finds out Sun Ho is the killer by asking witnesses and she tells detective. Detective Hyung Jo confirms the suspicions and gets himself arrested to avoid further killings since he is used by Sun Ho to carry all the blame. Sun Ho awaits Ga Hyun at her house. 

That's all the important things that happened up till now. 

Yeah I only used the last 3 timelines of the 8 since those actually matter to the group of resetters as far as we know. Now that I think about it.. I know this isn't the case thanks to Lee Shin still being unsure about certain things of the resetters but it would be messed up if the show revealed at the very end that this was already their second try.  Luckily this isn't true for this show as far as we know. 

I hope Hyung Jo will somehow live, either through reset-saving or just survival. 

Nice summary! I made one over on tumblr so I'll just add a couple of things I've been thinking about...

1. We don't know Sunho's motive yet. Every serial killer has a reason for choosing his targets but we don't know what his is. Idk if the show will answer this one for us.

2. Hyung Joo didn’t necessarily have to “save” Sungho this time around. As Lee Shin put it, that convict was always going to kill Hung Joo but always failed. She changed that fate in her 6th reset, but not in the 7th. So I think even if Hyung Joo hadn’t saved the lives of the judge & prosecutor and had faced up to the convict, Sunho would’ve lived either way. Which would ease his burden of guilt I guess. 

3. Hyung Joo surrendering means that either Sunho kills the cafe owner/Ga Hyeon and therefore clears Hyung Joo’s name as he’d be in custody at the time of the killing. Or it means he knows Sunho won’t kill either of them because it would expose himself. Either way, I’m pretty sure he’s got some sort of plan figured out with Ga Hyeon, there’s no way he’d put himself in shackles and leave her to Sunho’s mercy right?

4. I assume in her previous resets, Lee Shin never directly met Sunho but this time around she has, which puts her in more danger/into the unknown than she has been previously.

5. We still don’t know the identity of the mysterious professor Lee Shin always talks to. I thought it would turn out to be the old man but he just seems to be a spy. For now? Lee Shin’s daughter clearly doesn’t like him much. Maybe he still has more secrets.

Can't wait to find out the answers!