The manga ended earlier this year and had 59 chapters and there was a a small brake in the middle so they could end it there and then start up with a second season. So it really depends it could go ether way, I just hope that it isn't going to be like Berserk.
The one moe girl that you don't want to mess with!
That would be really stupid of them. They have the finished material, and it's only 60 chapters, so if there is filler, I can't see what possible purpose they could think it would serve.....unless they feel the kind of people who would watch mirai nikki require fanservice, in which case the anime industry is doomed