Can you hold a short position forever?
Well, yes. However, in reality no short position is held forever.
Your position can be closed for two reasons: either you’ll close it yourself when the market price of the asset you borrowed drops enough for you to make the profit you wanted to get, or it will be closed automatically because the price has risen too far. Of course, technically it’s possible that the price remains the same, but it’s more than highly unlikely. Alternatively, you can lose access to your trading account or forget that you opened a trade.