as one user to another, many have had the same question, try searching the questions under "fragments" and you can see those discussions.  Basically, they are not giving out much future hope of completing fragment portions or getting rid of all the clutter you have collected.  And they are going to make the pile even bigger.  Those lucky enough to finish their frags have them, the rest too bad.

I am working on the one in Arena Tag team, takes about 100 days, hopefully they will not quit on me, I am half done.

I wouldn't count on the game having another run of the events to get past fragments to be honest. They have sold fragments from past fragment summon champs before though. 

On the bright side: you'd eventually have an easier time with completing future fusions/fragment summons as you get stronger on your account. So focus on progression, be wise with resources, and hopefully you complete all future fusions. :)