The worst case scenario here would be simply not experiencing the effects of the Buprenorphine as the Naltrexone is a long-acting Opioid antagonist or "blocker". You don't need to be especially concerned here, as the only thing you will lose is the money spent on the Buprenorphine. Moving in the opposite direction, that is, taking Naltrexone or any other Opioid agonist like Naloxone, while under the influence of an Opioid agonist, will end the experience. If you are actually dependent upon Opioids, administering an Opioid agonist will produce powerful and immediate withdrawal known as Precipitated Withdrawal Syndrome.
You're right to ask questions, but in this instance you should not have anything to worry about.
Hey guys, I just realized I made a big mistake here. I got things reversed. Using Heroin following Buprenorphine will lead to a diminished effect whereas using Buprenorphine after Heroin can trigger precipitated withdrawal.