Yeah, but one of the reasons that he was depressed was that he isnt the leader of any powerful organization anymore (the other reasons being that his wife and son are both dead, and that his daughter hates him).

I agree. I know Laurel has been dead longer then Sara but hey Sara died over a year and so ago and she came out so hey miracles happen. also no one really knows how the pits actually work so you never know what might happen. just put her into one of them and hopefully it will work like it did for Sara. also I have another ideal, make black siren almost die and put her in the pit and then perhaps their spirits will meet on the other side and she give her earth 1 doppleganger another chance in life by giving her her body because it seems to me that black siren is beyond redemption at this point and I think her resting in piece on the other side with her dad and supposed sister (because we don't know if Sara has a earth 2 doppleganger and if she does, is she still even alive?) would be a better and fitting ending for her and let her at last be at piece. of course having john constatine be there and help the team find Laurel's soul on the other side and helping place it into black siren's body like they helped restored Sara's soul back into her body in season 4 would be another way to go as well. I have to say I'm glad they discovered more pits because now they are doing it like they did in the comics. so there are 3 more pits that we known of; there could be more that we don't know about of which I'm kind of happy about. as for Nyssa, Thea and roy heading out to destroy the 3 pits so they don't fall into the wrong hands is kind of a interesting story and having the thanatos guild join the show will be interested, they are kind of like a newly banded league of assiaisins. also the funny banter between Nyssa and Felicity was funny and Nyssa finally annulling her marriage to Oliver was actually overdue. As for Thea, I'm happy to see her now take on a more prominent role and get back into the action but sad to see her leave the show to.  hopefully like roy and Nyssa, she will make special guest appearances moving forward.

I was thinking they just find a way to restore Laurel's soul using another magic expert. Because putting Laurel inside Black Siren's body is just... weird.

I know but it still is a possibility. 

True but you never know with Nyssa. we know she destroyed the first pit after resurrecting Sara because she didn't like how she came out of it and with Laurel she might feel the same way but she's going to destroy it anyways so it doesn't fall into the wrong hands and they might as well use it to their advantage before hand. Look I'll be honest much like Sara having closure with her using the spear in Aruba I kind of feel like I have made my peace and she's gone and there's just no coming back to her but now that we know that there are more pits out there perhaps they should just do it and resurrect her and besides since her death, Sara tried to make it her mission to save her from death after she helped resurrected her from the dead. I think the team and Sara should return the favour. 

Not when soul swapping hasn't even been introduced as a concept. It also is magic based, alternate earths are sci-fi concepts.

She'll come back zombified though since she had been gone for multiple years now.