This could an issue with any deployment on your managed server, failing during the restart. So what could you do in such a case
1. Shut down both web logic servers manually.
2. Start them again manually.
3. By this time, your installer might have aborted giving you the continue, retry, abort options.
4. Then choose continue for the installer to finish the next steps.
Note: Even if the installer fails at this point, you could still consider the upgrade to be successful as the remaining steps would be just the upgrade of webcatalog which you could always perform even at a later time.
Hope this helps.