Seeing them again and then having to say goodbye again could be one of the most difficult challenges that Oliver has ever had to face (unless they’re total douches).
Given that Episode 100 will be part of The CW’s massive DC crossover, my guess is that the Moira who turns up will be the Moira from another Earth.
I won’t be shocked if the 101st episode features a decidedly gloomy Green Arrow.
The precedent was set when Barry jumped to Earth-2 last year on The Flash, so Oliver’s dead loved ones in Episode 100 could well be folks from Earth-3 or -4 or -5.