You can't safely assume that, but what are you going to do about it when it does fail? There is nothing you can do. There isn't usually a CloseClose function to use when Close fails. If Close fails, that's it. You're otherwise out of luck.
Certainly, in the write failure case where there is write failure you'd want to try writing to something else (ideally), notify someone that an operation didn't happen (as a last resort), or something to that effect in order to recover.
But in this case there is no need to try again and nobody really cares. Everything you needed the resources for is already successfully completed. If there is failure when releasing those resources, so what? There is nothing you can do about it.
Certainly, in the write failure case where there is write failure you'd want to try writing to something else (ideally), notify someone that an operation didn't happen (as a last resort), or something to that effect in order to recover.
But in this case there is no need to try again and nobody really cares. Everything you needed the resources for is already successfully completed. If there is failure when releasing those resources, so what? There is nothing you can do about it.