You want to pay their bills too while you are at it?
Cause I'm sure that a company who has a profitable product and service will randomly stop providing that product and service just for kicks.
Maybe not just for kicks, but I know that TV networks have killed highly rated shows for various reasons that wouldn't make sense to their viewers. I don't see this situation as much different.
I'm sure FFXI is still quite profitable for them, but they obviously feel they can make even higher profits and perhaps capture a more desirable demographic by shifting their resources to mobile games. Personally, I think they're in for a rude awakening.
As for the petition, I say don't stand in SE's way. Let them go through with this plan, and let it crash and burn. It will be the end of FFXI as we know it regardless of whether this endeavor succeeds or fails, but I think it's better for gaming as an industry if this sort of thing is proven to be a bad idea.