Oh God, I'd probably roll my eyes at any attempt to keep the Mane 6 around as actual characters. I hope they're just dead/gone. Anything else probably wouldn't feel right.
I honestly don't know how they're going to say "they're not here anymore and will never come back" without just implying they're dead (I feel like Hasbro wouldn't allow that it sounds kind of upsetting) but I'm sure they found a way.
What if the trailer drops and it's revealed the Mane 6 never existed at all in G5 and they're a television show like some theories a couple months back were saying? I wouldn't like that either.