Oh nice, there's a pretty good discussion brewing here, I hadn't thought to look here for it till just now.
Anywhoo, the last episode of this season is titled "Sacrifice". With what happened last week, that could end up meaning a lot of things.
From the Tommy discussion, I think one expectation is either that Borrowman's character will sacrifice himself for Tommy and entrust his legacy to him or Tommy will sacrifice himself for his dad. That seems to me what could be the big send off for next season.
Like wise, a few other possible sacrifices spring to mind. All could happen or none could happen. It feels like it's a little too early to "accurately" guess just now.
The other potential "sacrifices" that spring to mind are:
Thea some how sacrificing herself some how to save Roy in a way that he ends up as Ollie's sidekick / partner (In this case I don't even think she needs to die necessarily). That seems like a strong possibility.
Moira Queen sacrifices herself in some capacity to stop Malcolm's plans (this seems fairly likely to me just now).
Someone on the island sacrifices themself and seems to die (Slade or Shado in this case, probably most likely Shado in my mind just now).
Diggle sacrifices himself for .... something. Diggle is the biggest mystery right now because he's not based directly on any DC Character.