My new track has become a trend again. Tell me, how long will stand on it the label “trend” and what it depends on the duration of this icon?
Congrats! ! ! 
Congratulations!
I guess what it makes it stand with the icon is the traffic to your item compared to past days. Just have a look over your analytics and check if you have fluctuation.
If the file is not viewing - so will remove the icon?
yes, but the badge on your profile will stay.
I thought it depends on sales in a short time. Am I wrong?
Today icon “Lightning” was removed from the track 
@MaxRazumov If your item trends again, it will be back. The point of the “trending” badge is to show customers what items are currently deemed “exciting” based on several factors. It’s not intended as a permanent badge that stays there indefinitely. For more details about the trending badge, please see Introducing Trending and Recommendations on Envato Market. 