It is possible.
The Zephyr has two full sleeping cars - cars 531 and 532, plus eight(?) revenue roomettes in the dorm - car 540. When a car is removed due to equipment or staff shortages, car 532 is the one that goes. You could call and try to move your reservation to 531 or 540. Or just keep an eye on things by pulling up your reservation every so often to check. You could also occasionally check current roomette availability by starting a new booking online for your date between Chicago and Reno. Try eight passengers for then look for roomettes. If it shows a price, that means at least four roomettes are open. You can then up the room count from four to five, then incrementally up to eight to see if at least eight rooms are open. If it shows no availability for eight passengers, reduce the passenger count to 6 (at least three open), 4 (two open), or 2 (one open). If it you checked one day and there was good availability then tried again the next day and roomettes are sold out, that could be mean the 532 car and its 14 roomettes had been removed from the inventory for sale. A call to Amtrak to check your reservation status would be in order.
Amtrak not very good about timely notifications concerning reservation changes, so you are your own best advocate.