8th Ed. Troubling High Elves

It isn't Dwellers I'd be worried about so much as an initiative-testing spell (Pit of Shades most often with Elves), but that's where your opponent's most common lore choice comes into play. If they are using Life, then a strength test is going to suck for any large unit, but keep in mind, at best he's only getting to roll for 3 spells without a lord (lv2 with a Silver Wand... which granted is going to get Dwellers just over half the time). Shadow would worry me a lot more with Saurus or a Stegadon though.

The Diadem of Power won't be able to provide perfect defense, but if one of Winds of Magic dice is a 1, 2 or 3 (even better if both are), then you should still be in pretty good shape and at least have a shot at stopping the big stuff. Unless it's dire (i.e. casting Flesh to Stone and/or the regen spell into an important combat), save your dispel dice for Dwellers if you're facing life and worry about taking off the RiP spells in your magic phase if they can wait. If they do get off a game changing spell, then all you can do is shrug it off and wait for the next game.

As for the Stegadon, I know they work well for a lot of people, but it's hard for me to get around the point cost considering even a basic Stegadon is about the same point total as the Skrox unit I listed and will severely limit the other things you can take at 1400 points. Getting stuck in a unit of Elves at this point total isn't as likely, but roll badly on the charge with impact hits and thunderstomp, especially against Phoenix Guard, and you are probably going to lose combat (even worse in subsequent rounds without the impact hits).

HE are a rough match up at this point total with the restrictions you've been given. Just try and look at it as a challenge and do what you can to exploit the small mistakes your opponent makes. The nice thing about Warhammer is there is no "best" way to play any of the armies, so ultimately, you need to go with what works for you.

By the way, how are the restricted units determined (i.e. did you get to pick which special choices you get to use)?