The Ireactions idea of later episodes being a seperate group of Sliders works for me.
Rather than a "All a Dream"/"Never Happened Moment" we can have a side by side approach.
The Non Native Earth Quinn is a seperate Quinn, or the Cromagg Deception re Charlie was less a Knowing Spy and more of a Sleeper/Manchurian Candidate.
Maybe there was a real Quinn who came from invasion world just not OUR Quinn...
A Quinn who discovered Sliding in 95 does not have to be totally written off but a gentle handwave avoiding how this is orriginal Quinn may be best with maybe subtle hints later in the Series to spark debate among Fans but remain Unanswered.
New Sliders to Join him would be fine but as you say careful casting for Chemistry would be essential.
I doubt Sabrina will come back as a full cast member but a Cameo may be possible if in the right spirit perhaps is viable.
Arturo coming back as a Mentor or even a Rival Mentor for Mature Quinn is also possible with the Blue Gate Arturo situation.
What if Gillian of the Spirits Quinn never reunited with our Core Group but a Very Similar Double did? That could be interesting to play with.
Quinn exploring our World and Rediscovering it is his own could be an interesting Pilot. Reconciling the Changes to our World with his Memories of Home.... His almost Idealised Home could be very engaging.
"It's only a matter of time. Were I in your shoes, I would spend my last earthly hours enjoying the world. Of course, if you wish, you can spend them fighting for a lost cause.... But you know that you've lost." -Kane-