The War Wizard gets the Durable Magic feature at 10th level which states:
[…] While you maintain concentration on a spell, you have a +2 bonus to AC and all saving throws.
The Ready action states:
[…] When the trigger occurs, you can either take your reaction right after the trigger finishes or ignore the trigger. Remember that you can take only one reaction per round.
When you ready a spell, you cast it as normal but hold its energy, which you release with your reaction when the trigger occurs. To be readied, a spell must have a casting time of 1 action, and holding onto the spell’s magic requires concentration. If your concentration is broken, the spell dissipates without taking effect. […]
Thus a War Wizard with a Readied spell would gain bonuses to their AC and saving throws. But what happens if the Wizard chooses to make an opportunity attack or use their reaction on something else? Do they maintain concentration on fire-bolt or do they drop concentration; Do they continue to benefit from Durable Magic or not?
The only thing I was able to find was that the Sage Advice Compendium document (pdf link) states the following (emphasis mine):
Q. I have a readied action. Can I stop readying to take an opportunity attack? Or is ready a full turn commitment?
A. If you have an action readied, you can make an opportunity attack, which causes you to stop readying.
Notably, this only addresses opportunity attacks and doesn’t give any justification, so part of my question is this: Is there support for the conclusion made in the Sage Advice Compendium anywhere in the rulebooks themselves?