Not at all, it is common to have the resistor fail while the motor is fine still, or vice-versa in this case, and the question that remains is, does the resistor continue to work properly? If it does, it does not need replaced. As I stated previously, there is no penalty in replacing a faulty blower and continuing to use a working resistor module. You gain nothing replacing a working part based only on internet false information. Either the resistor has failed or it hasn't. There is no reason to plan to replace both until the new motor is installed to check for proper operation.
If the resistor module works today, if it fails at some point in the future, there is no extra cost, no extra labor, no detriment to not continuing to use the resistor module if it still works today... unless you're in the camp that wants to replace everything remotely related to a fault but then, where does that end? Motor blows, so replace transmission?
Fortunately there is observation and testing so we can only replace faulty parts. It might be different if while replacing the one part, it made replacing the other a lot less work and/or expense, but I don't see any evidence of that in this case and it usually isn't much work to replace the blower motor speed controller.
On the contrary, this seems like the sort of scam argument that a shop looking to maximize their profits would make, telling someone "oh you need to replace this other part now too", when it is not true, and the other part has minimal real labor, and a high markup so it's just a big profit margin for the shop to pretend that is needed.
To word it differently, a new motor does not in any way pose additional stress on a working speed controller. If the speed controller works with the new motor, it would be paranoid/madness/misinformation to replace a part that is demonstrating that it is working fine.
