I would like to discuss my thoughts and predictions about Silas.
First, I don't think they're gonna make Silas succeed in getting rid of The Other Side. Because if every single supernatural being to have ever been on the show comes back, there will be simply too many possibilities for the show. That wouldn't make sense, at least to me.
However, there's the possibility that Silas does not actually know what will happen if The Other Side gets "broken", and it might not bring back everyone like Silas says he it will. Think about it... First, it's never been "broken" before; secondly, if Silas was already buried when Qetsiyah created The Other Side, then he might have little idea of how it was created.
There's also the possibility that Qetsiyah will stop Silas from taking the Cure once he destroys The Other Side. Qetsiyah was a supernatural being herself, and she never found peace as Silas never took the cure. If she's been watching him from The Other Side from 2000 years, she might be waiting for the day he destroys The Other Side and brings her back so she can stop him from finally passing on and re-create The Other Side.
Now, if the main characters are gonna kill Silas and stop him from destroying The Other Side, they're gonna have to find his weakness, if he has any. But if the spell that Qetsiyah used really is the same as the one that Esther used, then he must have one. It seems that you need to use something that comes from nature for the spell to work... For the Originals, it was the White Oak Tree. What did Qetsiyah and Silas use to create their spell for immortality? But then again, the spell that was used on Silas seems to be different, more powerful too. It makes sense, since Silas and Qetsiyah were apparently much more powerful than Esther. But if Silas has no weakness, then I don't think the main characters will be able to defeat him anyhow, at least given the information that we currently have about the story. It will either be Qetsiyah, or they will find his one weakness, or a completely new variable will be introduced in the show that will change everything.