My theory see how this goes :
Mike comes back jessie and walt are about to be executed and mike realises maybe walt was right gus is going too far this time especially as he has grown quite attached to jesse.
Mike kills tyrell walt grabs tyrells gun shoots gus and gus dying tells jesse
truly or maybe as a last dig at walt it wasnt him who poisoned the kid it was walt and series ends same as last time jesse gun in hand walt shocked BANG.
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