To answer your question, I would feel the same about the release (not that worried about it because I believe Gliscor will return), but would not be quite as excited about the new addition. Getting Gible is more exciting than catching a Gligar.
Considering where we currently stand with Ash's team and Gliscor's release, would you prefer that Gligar was never caught? And if so how do you see the events that She was involved in with Gliscor?
Personally I could see Ash calling back one of his reserves to have the 6 on 6 with paul, either Snorlax, Tauros, Muk, Heracross, Glalie, or Donphan would of been used to fill that 'filler' spot. Ash's gym team vs Byron would have been : Chimchar/Grotle/Buizel, and his team against Candice would be : Chimchar/Pikachu/Staraptor/Buizel.
Other than those three events the only other changes would be some more character development for other team members.