I normally play on expert, but I know destro can become quite weak at the high 40s, and even more so after level 50.

Anyway, I was interested in playing a mage who uses destruction. No illusion, probably some kind of armor (recommendations welcome) and a little conjuration here and there. Enchanting as well, obviously. I do not want 100% reduction though, maybe about 60-70% only.

Anyway, would it be doable? I would hate to spend all that time only to realize that after level 50 it is useless.

Destruction is fine, even on master, especially with conjuration.

I've done it with a dead is dead character and that character was level 72 when I stopped using him. You will want higher than 60% destruction cost reduction. By level 40 I would want at least 75% reduction especially on expert or master. By 50 you will want 90% reduction.

This is because by level 50 your primary spells will be incinerate and thunderbolt. You will be dual casting them... which with either spell nets close to 200 damage per hit when fully perked. However even with perks and 50-70% cost reduction and a lot of magicka you won't get many casts before you are out of magicka. Think about it, even if you get the spell down to 50pts dual cast and you have 400 magicka you are only going to get 8 casts. On adept most level 50 enemies will take 3-5 hits each with dragons and priests taking even more so in a crowd you will run out quick. On master that is going to turn into 6-10 hits per enemy. You will want 90% reduction, and I understand not wanting 100% but those expert destruction spells are VERY expensive to dual-cast.

Conjuration is the perfect skill for master... because it is the only skill that automatically improves with the difficulty setting. If you play on master your conjurations also get more health and do more damage. A dremora lord on master will slaughter bandits the same as one on novice .

from what i'v played on adept, a butter knife is all you would need to be a badass at any level and any small bit of conjuration will make almost any build viable

Depends on what you mean by a little conjuration. A conjured familiar is a "little conjuration" and is useless; dual Dremora lords is not what anyone would consider a little conjuration but it makes you a badass. From what I've seen a pure destruction mage or pure anything is kinda hard to do. You need to have some competency with a couple of other skills in order to have a viable build.

It's perfectly doable. I have two straight mage characters and play just fine on normal difficulty.

Yes destruction is not really useless as some say, especially on adept though it isn't the best either,