For the most part, I like it. I think giving them an arcane bond as a sacred weapon feels like a nice fit. However, I have two big issues with it.
1) Giving them the wizard/sorcerer list is a massive buff. Prohibiting evocation magic doesn't put a dent in that. Especially for a class that can swift-action spells. You're still swapping a class list mostly with combat buffs and out-of-combat utility for the best spell list in the entire game. I know you wanted to avoid it, but magus list fits better.
2) I don't think the archetype should get spell combat. In fact, I'm baffled why you gave them spell combat. You said you didn't want to steal too much from the magus and yet you stole their primary class feature. And all they lose is sacred armor, which is one of the worst class features the warpriest has.
Change the list to the magus list and get rid of spell combat, and the archetype would be great.
I like:
1. Bonded Weapon
2. Armored Spellcasting progression
3. Opposition School
I don't like:
1. Switching INT for spells but keeping WIS for fervor and blessings. Add a feature at the beginning that converts all the WIS related things to INT and call it a day.
2. "Necromantic Fervor". The name doesn't resonate too well with me and I am not in love with the temporary HP idea... that's more of a "false healer" thing to me. How about making Fervor a pool of elemental energy that you can release as a touch attack, and you can spend 2 uses to add it to an attack ala Elemental Fist? (I.e., you announce it and then if the attack misses you lose the charges anyway).
3. I don't like Fervent Casting either, I submitted an idea on point 2 that might be a good replacement. In any way, we know they will be using fervor for swift action casting anyway, so they won't need to concentrate.
4. Losing Bonus Feats. Bonus Feats are ultra important to make the fun builds. I think they should keep them. Let the Magus keep Arcana for themselves.
I'm not entirely sold on:
1. Sorc/Wizard list. I think it would be better with the Magus list.
Okay, sure. That's good feedback. Regarding point 1, what do you think of the magus list, plus a bunch of buff spells? I really want a more defensive or protective flavour, and the magus list isn't doing it for me. Recommendations of spells would be great.
As for point 2, is it really? I thought that spellstrike was more important, and also that a warpriest would have less use spell combat since they could already fervor spells out, but I can for sure change that. To tell you the truth, I've never played a magus, so thanks for letting me know. It is heavily delayed spell combat... On the other hand, this archetype seems to take up too much page space, so maybe I should omit an ability entirely.
I played two magi, one of them in a long term game, and ran a three-year campaign with a magus in it. The magus spell list is full of defensive buffs like mirror image, vanish, shield, and a few mobility items like bladed dash. It's designed specifically for a melee fighting class, so it works very well for a warpriest. Especially considering bladed dash would work with fervor.
Spellstrike gets a lot of attention, but spell combat defines a magus. It lets you attack and cast spells at the same time. The warpriest already has a class feature that lets them do this in their own way. So giving them spell combat is superfluous at best and gives too much power at worst. I recommend nixing it entirely. The archetype still feels worthwhile anyway.
It's an alternate class, not an archetype. Those are rare. Well done!