There's kind of a double edged sword there. If Slade gives Ollie a choice and he manages to save both, then Slade/Deathstroke will come across as just another pathetic villain who can't carry out a simple plan/threat.
However, if Arrow fails to save both, it would reflect badly on him.
I'm really really hoping they don't go that route of Slade giving Ollie a choice. It would be fairly predictable and boring writing. Besides, Deathstroke should be way more badass.
I really hope Arrow (the show) strays completely from the comic books and carves out its own destiny, which gives the writers more freedom for genuine surprises and creativity.
I want Slade to actually follow through on his threats. He needs to totally upset Oliver's life by the end of the season, in more ways than 1. I'd love too him do all of the following -
1. kill someone (or multiple people) close to Oliver (preferably Laurel who isn't working at all as is and perhaps Moira too - which could be especially poignant if done right).
2. Turn the general populace of Starling city and even Queen Consolidated against Oliver.
3. possibly render the Queen family broke
4. Take a prisoner ( maybe Laurel or Roy) who he will train and convert to a major villain for the future.
5. Cripple some of team arrow - injure Black Canary (Sara) and John Diggle - and frighten the crap out of Felicity.
6. Leave the city shattered, take his prisoner away and disappear for like a whole season, to return just as ollie has finally pulled his life back together and Team Arrow is finally full steam ahead once more.
Forget the comics, the writers should focus on what works well in the show (Team Arrow, Sara as BC, SLADE) and filter out what doesn't ( LAurel, Roy, etc). Manu Bennett is awesome in the role and Slade has been there since basically day one...he would fill the shoes of Arrow's primary nemesis brilliantly. Have him serve as the one wreaking personal havoc on Ollie's life throughout the series, not just as a one season only big bad who dies in the finale. I'd much rather see Slade cause hell then leave for an extended period so the show can involve other villains, but bring him back later at different times in short bursts.