I believe the possibility of FFX becomming redundant due to Tidus' return is ver possible because it does make alot of sence since Tidus had a chance to return and he did so couldn't everyone else as well as for reading into this too much thats what video games are for you get to play them then explore the possibilities of well what if this happened or that and in your mind you can think of 100s of ways things could have been better or even worse I know for a fact that in Baldurs Gate Dark Alliance I have thought of serveral different possibilities or even in the new FF13 game FF13-2 you can change the way things are I have beaten the game dozens of times yes I haven't done it all at once because i've had no time hence why I left 3 years ago but I explored all the possibilites in the game then thought of things Square Enix could have done things differently but as for the other ressurections in my opinion it is entirely possible and would have made an interesting turn in the storyline