While I would have preferred the full sized Lily becoming Gajeel's bro', I don't really have any problems with this outcome. I'm sure we'll see Panther Lily return to his buff form, although probably temporarily, at some point in the future.
Now, Mashima basically just brought Lisanna back to life. It's hard to believe any significant death can or ever will occur in this story anymore. I'm mildly interested in Lisanna's interaction with the guild, but I still do not like that Mashima decided to do that.
I'm hoping she only sticks around for a while before they send her back somehow.