I have started working my way through the Legendary missions in story mode and am part way through 4-1. I had a character facing Longtooth as a summon on an enchanter and selected the summon monster spell than cancelled it and went with Sign of Wrath instead. After rolling the dice a monster was summoned anyway and a fight occured. Then it came up with the option to evade or continue from sign of wrath. I chose continue and couldn't go any further. I restarted the game, went back in to story mode and again it comes up with the option to evade or continue. No matter which one I choose I cannot go any further or select anything else. Not even the vault or settings menu (although it makes the sound when I select those buttons). Because I cannot select the settings cog I cannot even forfeit the mission to try again. I have tried clearing the cache, but have not cleared the game data yet as I am afraid I will loose my game progress. What are my options to retain my progress and be able to continue playing story mode?

If anything else does not help. Delete the party and form a new by using same characters from the experinced characters.

Will I need to redo all my story progress if I do this?

You will be able to access the higher adventures based on the "completion" of the characters in your party - for example since you reached 4-1, you should be able to start there.  But I think you lose the heroic/legendary completion records so you'd have to start over if you're trying to get the reward for completing everything on heroic/legendary.

I had made it through almost everything (Through to 6-5) on Normal, most on Heroic and was working my way through Legendary for the bonus unlocks.