Will I be able to mount my TrueCrypt partition/container after I reinstall or upgrade the operating system?
 
Yes, TrueCrypt volumes are independent of the operating system. However, you need to make sure your operating system installer does not format the partition where your TrueCrypt volume resides.
 
Note: If the system partition/drive is encrypted and you want to reinstall or upgrade Windows, you need to decrypt it first (select System > Permanently Decrypt System Partition/Drive). However, a running operating system can be updated (security patches, service packs, etc.) without any problems even when the system partition/drive is encrypted.