Time Frame

• According to YouTube's Username Policy, an account is considered inactive if it has not been used within six months. YouTube may also consider an account inactive if the channel has never had a video uploaded to it, or if there no evidence that the user has watched other videos, commented on other channels or otherwise engaged in the YouTube experience in six months.
  
  

What Can Happen

• If YouTube discovers an inactive account, it will, according to its Username Policy, "reclaim" the account. YouTube says they will not give notice that this is occurring. However, with so many videos being watched each day, it's not likely that YouTube will get wind of an inactive account unless someone reports the problem.
  
  

Name Squatting

• You may find that an inactive account has a username you might want to use. If someone takes a name and "squats" on it -- in other words, just takes the name and doesn't do anything with it -- you could contact that user via direct message and ask him to give you the username. If that doesn't work and the username appears totally abandoned, try contacting YouTube Partner Support to ask if you can take over the channel.
  
  

Trademark Complaints

• One instance in which a YouTube account could be flagged as inactive and taken down is in the event that someone complains about trademark infringement. While YouTube claims that taking someone else's brand name as your username is not a violation of trademark, it can naturally cause some confusion among potential customers. If the "fake" account is posing as the real company, even if it's just by imitating the look of the real company's channel and not by posting actual videos, the actual company may have recourse to have the fake one removed. The first step is to try to contact the user by direct message through their channel; the second is to use YouTube's Trademark Complaint form.