Well , I wouldn't mind an Earth 2 here (Jay Garrick is rumored to be coming)Really? Because that would be as awful as Dallas' "dream season". You have to own your mistakes and learn from them instead of taking the easy way out. Anyway, is not going to happen, it seems they will deal with the consequences of Olivers' actions on Season 4:
Agreed, is dumb to repeat the same Sara-is-dead-now-Sara-is-alive plot twice, is going to be awkward to see Laurel and Quentin's reactions. And if the producers repeat the same mistakes, Oliver will lie about Sara being alive, so Laurel and Quentin will get angry with him and more forced drama... again!!
Like I said not long ago, it would've been smarter to use the concept of the Multiverse to introduce a Sara Lance from Earth 2 who is the White Canary or Manhunter there, this way, death still matters and doesn't become an example of bad writing like in the comics. But the damage is done, so hopefully, Sara's resurrection will come at a heavy price, it would make it more interesting and justify why Tommy and Moira should remain dead.
but I hope they get through Ollver, Laurel and Quentin's reaction to Sara's resurrection before LOT shows up. The spinoff looks great, However you are right and there is a distinct possibility of the Arrow writers screwing things up with the same mistakes.