He's going to die lvl 1, be dead for 10seconds and then just TP back to lane before fiora hits 2. All he literally has to do is play it safe till then and wait for assistance. Which in, you can then go to help him out as 2v2ing with a Darius is much, much better than 2v2ing with a Fiora. He'll most likely get 5 stacks and be a forced to be reckon with.
There's a reason he's dominating top lane right now. That isn't to say he might not have a brain to do so... but he should be fine, especially if he plays defensively. Tbh, you can really only abuse a Darius that screws up on his own. Playing against a passive Darius is some times worse than an offensive one.