I'm really enjoying the game, and while I accept the dev's decision to make permadeath equate to campaign failure/restart, I'm sure many people agree having permadeath option like vanilla XCOM would add a lot more gameay replayability.

Several things to consider:
1. Agents that die simply die (aka permadeath) but you can continue your campaign
2. You can use Androids to fill in APC soldier slots (but only if you have less than 4 total soldiers)
3. Androids can be upgraded with Schematics (effectively becoming one of the 11 soldier classes) - but only 1 Android can use a single Shematic at a time (keeping the concept of having 11 unique characters)
4. Installing a Schematic allow that Android to gain XP
5. You can't remove a Schematic from an Android, but you can rebuild the Schematic if the Android dies
5. The campaign fail state is if you can't fill in the APC 4 unit roster (ie if you don't have money to build more Androids)
6. Still keep the reinforcement Android mechanic to replace a downed solider during missions
7. You can fail missions (except for the key missions eg final mission for each group) leading to the usual negative outcomes
8. Evac zones can be called to abandon a mission but save your soldiers (except for key missions)
9. Androids killed in battle stay dead too (rather than the current of being fixable for small fee)

I haven't finished the campaign so I assume there might be wierd cutscenes of long dead soldiers but I think this is acceptable or if you're playing on Permadeath, you're done with the story and just want to focus on gameplay anyway.

The above may need some balancing but I think it achieves the permadeath concept without requiring too much gameplay changes.