Well, I guess it depends in part on why you're playing. If you're really into tactical play (which I kinda get the vibe that you are?) and battles as the "meat" of the game, switching out characters regularly would probably be less of a big deal.
I think, particularly now with these big APs, that a lot of players like to experience the full hero's journey. Like watching Luke go from whiny farmhand to blowing up the Death Star with his eyes closed. They enjoy the progression. If you keep swapping out PCs, you never get that satisfaction, but the people who are cool with that are getting their enjoyment elsewhere.
Whatever floats your boat & all that. FWIW, I didn't really expect our PCs would survive this AP, so I'll hardly be bent out of shape if you kill Surana.