I have a LAX-ORD-FCO flight coming up in a few weeks on saver award tickets on which I purchased Economy Plus Essentials for $339/person, which is E+ and an extra checked bag. For two people this is a healthy chunk of change for 3 more inches of legroom.
Yesterday I got a notice that there was a 12-minute schedule change on the LAX-ORD leg. I happened to look at the reservation today and saw that my seat assignments were missing. I tried to add them back and it wanted to charge me $308/each for the seats and no option for the Economy Plus Essentials. So I called and, to make a long story and 2 CSRs hanging up on me short, the schedule change caused my EPE purchase to be canceled and refunded. Talking to the CSRs there was no way they would be able to add it back to my reservations since it's a one-time only offer. Normally, I was told, they would just cancel the reservation and have me start over but there was no more saver economy availability on this itinerary. (I did ask if they would open saver J availability but that was immediately shot down. Doesn't hurt to ask...) After I was hung up on a second time, the CSR on call #3 was able to immediately help. She put me in the E+ seats I originally requested at no charge so now I only need to pay for the second bag at $100/each, which is far cheaper than what I was paying before.
So the moral of the story is: if you have a schedule change they might/will cancel your EPE with no recourse but eventually you might get ahold of someone who will give you a better deal than you had before.